Structure material

ABSTRACT

A structure material includes a resin, reinforced fibers, and voids. The structure material includes a volume content of the resin being within a range of 2.5% by volume or more and 85% by volume or less, a volume content of the reinforced fibers being within a range of 0.5% by volume or more and 55% by volume or less, the voids being contained in the structure material in a rate within a range of 10% by volume or more and 97% by volume or less, a thickness St of the structure material satisfying a conditional expression: St≥Lf2·(1−cos(θf)), and a specific bending modulus of the structure material represented as Ec1/3·ρ−1 being within a range of 3 or more and 20 or less, and a bending modulus Ec of the structure material being 3 GPa or more.

FIELD

The present invention relates to a structure material including a resin,reinforced fibers, and voids.

BACKGROUND

In recent years, market demands for improvement in stiffness andlightness are increasing year by year for industrial products such asautomobiles, aircraft, and sporting products. To meet these demands,fiber-reinforced plastics excellent in stiffness and lightness arewidely used for various kinds of industrial applications. Specifically,to satisfy lightness, use of core materials having lightness is widelystudied (refer to Patent Literature 1 and Patent Literature 2). However,core materials are significantly poor in stiffness as a single material.For this reason, use of a core material requires product design such asarrangement of a skin layer having high stiffness on the outer peripheryof the core material. However, products designed in that way inevitablyincrease in mass or increase in thickness. In other words, even ifresultant product weight reduction is achieved, its contribution issignificantly restricted. Meanwhile, structure materials having voidshave characteristics such as thermal insulation, sound insulation, andenergy absorption apart from lightness and are thus also widely used forvarious kinds of industrial applications (Patent Literature 3 and PatentLiterature 4). However, structure materials having voids are alsoinferior to other structure materials in stiffness as is the case withcore materials and are thus restricted in their sole use as structurematerials. From the foregoing circumstances, a pressing need is toprovide a structure material excellent in stiffness and lightness.

In recent years, market demands for improvement in lightness areincreasing year by year for industrial products such as automobiles,aircraft, and sporting products. To meet these demands, fiber-reinforcedplastics that are light and excellent in mechanical characteristics arewidely used for various kinds of industrial applications. Specifically,to satisfy lightness, use of core materials having voids is widelystudied (refer to Patent Literature 1). However, core materials havingvoids are significantly poor in desired mechanical characteristics. Forthis reason, use of a core material having voids requires product designsuch as arrangement of a skin layer having high stiffness on the outerperiphery of the core material in order to compensate for the inadequatecharacteristics. However, products designed in that way inevitablyincrease in weight. In other words, even if resultant product weightreduction is achieved, its contribution is significantly restricted.Meanwhile, structure materials having voids and/or density differencehave characteristics such as thermal insulation, sound insulation, andenergy absorption apart from lightness and are thus also widely used forvarious kinds of industrial applications (Patent Literature 5 and PatentLiterature 6). However, structure materials having voids and/or densitydifference are also inferior to other structure members in mechanicalcharacteristics as is the case with core materials and have been thusrestricted in their sole use as structure materials. From the foregoingcircumstances, a pressing need is to provide a structure materialexcellent in lightness and mechanical characteristics.

CITATION LIST Patent Literature

-   Patent Literature 1: WO 2014/162873-   Patent Literature 2: WO 2015/029634-   Patent Literature 3: Japanese Patent Application Laid-open No.    2015-39842-   Patent Literature 4: Japanese Patent Application Laid-open No.    2015-30755-   Patent Literature 5: Translation of PCT Application No. 2014-508055-   Patent Literature 6: Japanese Patent Application Laid-open No.    H06-320655

SUMMARY Technical Problem

The present invention has been made in view of the above problems, andan object thereof is to provide a structure material excellent instiffness and lightness.

Another object of the present invention is to provide a structurematerial excellent in lightness and mechanical characteristics.

Solution to Problem

A structure material according to a first mode of the present inventionincludes a resin, reinforced fibers, and voids. The structure materialincludes a volume content of the resin being within a range of 2.5% byvolume or more and 85% by volume or less, a volume content of thereinforced fibers being within a range of 0.5% by volume or more and 55%by volume or less, the voids being contained in the structure materialin a rate within a range of 10% by volume or more and 99% by volume orless, a thickness St of the structure material satisfying a conditionalexpression: St≥Lf²·(1−cos(θf)) where a length of the reinforced fibersis Lf and an oriented angle of the reinforced fibers in a sectionaldirection of the structure material is θf, and a specific bendingmodulus of the structure material represented as Ec^(1/3)·ρ⁻¹ beingwithin a range of 3 or more and 20 or less where a bending modulus ofthe structure material is Ec and a specific gravity of the structurematerial is ρ, and the bending modulus Ec of the structure materialbeing 3 GPa or more.

A structure material according to a second mode of the present inventionincludes a resin, reinforced fibers, and voids. The structure materialincludes a volume content of the resin being within a range of 2.5% byvolume or more and 85% by volume or less, a volume content of thereinforced fibers being within a range of 0.5% by volume or more and 55%by volume or less, the voids being contained in the structure materialin a rate within a range of 10% by volume or more and 99% by volume orless, a thickness St of the structure material satisfying a conditionalexpression: St≥Lf²·(1−cos(θf)) where a length of the reinforced fibersis Lf and an oriented angle of the reinforced fibers in a sectionaldirection of the structure material is θf, a specific bending modulus ofa first part of the structure material represented as Ec^(1/3)·ρ⁻¹ beingwithin a range of 1 or more and less than 3 where a bending modulus ofthe structure material is Ec and a specific gravity of the structurematerial is ρ, and a specific bending modulus of a second part of thestructure material different from the first part being within a range of3 or more and 20 or less.

In the structure material according to the first mode of the presentinvention, the bending modulus Ec of the structure material is 6 GPa ormore.

In the structure material according to the second mode of the presentinvention, the bending modulus Ec of the second part of the structurematerial is 6 GPa or more.

In the structure material according to the second mode of the presentinvention, the first part and the second part of the structure materialare present at different positions in a thickness direction of thestructure material.

In the structure material according to the second mode of the presentinvention, the first part and the second part of the structure materialare present at different positions in a planar direction of thestructure material.

In the structure material according to the first and second modes of thepresent invention, a specific gravity ρ of the structure material is 0.9g/cm³ or less.

In the structure material according to the first and second modes of thepresent invention, a porosity of parts within 30% to a midpoint positionin a thickness direction from surfaces of the structure material iswithin a range of 0% by volume or more and less than 10% by volume, anda porosity of a residual part is within a range of 10% by volume or moreand 99% by volume or less.

In the structure material according to the first and second modes of thepresent invention, the reinforced fibers are coated with the resin, anda thickness of the resin is within a range of 1 μm or more and 15 μm orless.

In the structure material according to the first and second modes of thepresent invention, the reinforced fibers are discontinuous and aredispersed in a nearly monofilament form and in a random manner.

In the structure material according to the first and second modes of thepresent invention, an oriented angle θf of the reinforced fibers in thestructure material is 3° or more.

In the structure material according to the first and second modes of thepresent invention, a longer of the mass mean fiber length of thereinforced fibers is within a range of 1 mm or more and 15 mm or less.

In the structure material according to the first and second modes of thepresent invention, the reinforced fibers are carbon fibers.

In the structure material according to the first and second modes of thepresent invention, the resin contains at least one thermoplastic resin.

In the structure material according to the first and second modes of thepresent invention, the resin contains at least one thermosetting resin.

Advantageous Effects of Invention

The structure material according to the present invention can provide astructure material excellent in stiffness and lightness. In addition,the structure material according to the present invention can provide astructure material excellent in lightness and mechanicalcharacteristics.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a sectional structure of a structurematerial according to first and second modes of the present invention.

FIG. 2 is a schematic diagram of an example of a dispersion state ofreinforced fibers in a fiber-reinforced mat used in the presentinvention.

FIG. 3 is a schematic diagram of an example of sectional structures in aplanar direction and a thickness direction of the structure materialaccording to the first and second modes of the present invention.

FIG. 4 is a drawing of parts within 30% to a midpoint position in athickness direction from surfaces of the structure material and aresidual part.

FIG. 5 is a drawing of parts within 30% to the midpoint position in thethickness direction from the surfaces of the structure material and theresidual part.

FIG. 6 is a schematic diagram of an example of an apparatus formanufacturing a fiber-reinforced mat.

DESCRIPTION OF EMBODIMENTS

The following describes a structure material according to first andsecond modes of the present invention.

[First Mode]

First, the following describes the structure material according to thefirst mode of the present invention.

FIG. 1 is a schematic diagram of a sectional structure of the structurematerial according to the first and second modes of the presentinvention. As illustrated in FIG. 1, this structure material 1 accordingto the first mode of the present invention includes a resin 2,reinforced fibers 3, and voids 4.

Examples of the resin 2 include thermoplastic resins and thermosettingresins. In the present invention, a thermosetting resin and athermoplastic resin may be blended with each other; in that case, acomponent with an amount exceeding 50% by mass of the componentscontained in the resin is the name of the resin.

In one mode of the present invention, the resin 2 desirably contains atleast one thermoplastic resin. Examples of the thermoplastic resininclude thermoplastic resins selected from crystalline plastics such as“polyesters such as polyethylene terephthalate (PET), polybutyleneterephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylenenaphthalate (PEN), and liquid crystal polyesters; polyolefins such aspolyethylene (PE), polypropylene (PP), and polybutylene;polyoxymethylene (POM), polyamide (PA), and polyarylene sulfides such aspolyphenylene sulfide (PPS); polyketone (PK), polyether ketone (PEK),polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyethernitrile (PEN), and fluorine-based resins such aspolytetrafluoroethylene; and liquid crystal polymers (LCP)”, amorphousplastics such as “styrene-based resins, polycarbonate (PC), polymethylmethacrylate (PMMA), polyvinyl chloride (PVC), polyphenylene ether(PPE), polyimide (PI), polyamideimide (PAI), polyetherimide (PEI),polysulfone (PSU), polyether sulfone, and polyarylate (PAR)”,phenol-based resins, phenoxy resins, polystyrene-based,polyolefin-based, polyurethane-based, polyester-based, polyamide-based,polybutadiene-based, polyisoprene-based, and fluorine-based resins,acrylonitrile-based and other thermoplastic elastomers, and copolymersand modifieds of these. Among them, polyolefin is desirably used in viewof the lightness of an obtained structure material, polyamide isdesirably used in view of the strength thereof, amorphous plastics suchas polycarbonate and styrene-based resins are desirably used in view ofthe surface appearance thereof, polyarylene sulfides are desirably usedin view of heat resistance, polyether ether ketone is desirably used inview of the continuous use temperature thereof, and fluorine-basedresins are desirably used in view of the chemical resistance thereof.

In one mode of the present invention, the resin 2 desirably contains atleast one thermosetting resin. Examples of the thermosetting resininclude unsaturated polyesters, vinyl esters, epoxy resins, phenolresins, urea resins, melamine resins, thermosetting polyimides,copolymers and modifieds of these, and resins obtained by blending atleast two of these. The structure material according to the presentinvention may contain impact-resistant improvers such as elastomer andrubber components and other fillers and additives to the extent that theobjects of the present invention are not impaired. Examples of fillersand additives include inorganic fillers, fire retardants, conductivityimparting agents, nucleators, ultraviolet absorbers, antioxidants,damping materials, antibacterial agents, insect repellents, deodorants,anti-coloring agents, thermal stabilizers, mold release agents,antistatic agents, plasticizers, lubricants, colorants, pigments, dyes,foaming agents, anti-foaming agents, and coupling agents.

The volume content of the resin 2 is within a range of 2.5% by volume ormore and 85% by volume or less. When the volume content of the resin 2is less than 2.5% by volume, it is unable to bind the reinforced fibers3 within the structure material 1 together to make the reinforcingeffect of the reinforced fibers 3 sufficient and to satisfy themechanical characteristics especially bending properties of thestructure material, which is thus undesirable. In contrast, when thevolume content of the resin 2 is larger than 85% by volume, the resinamount is too large, and it is difficult to have a void structure, whichis thus undesirable.

Examples of the reinforced fibers 3 include metallic fibers formed ofaluminum, brass, stainless, and the like, polyacrylonitrile (PAN)-based,rayon-based, lignin-based, and pitch-based carbon fibers, graphitefibers, insulating fibers formed of glass and the like, organic fibersformed of aramid, phenylenebenzobisoxazole (PBO), polyphenylene sulfide,polyester, acrylic, nylon, polyethylene, and the like, and inorganicfibers formed of silicon carbide, silicon nitride, and the like. Surfacetreatment may be applied to these fibers. Examples of the surfacetreatment include coating treatment with metal as a conductor, treatmentwith coupling agents, treatment with sizing agents, treatment withbinders, and adhesion treatment for additives. One of these fibers maybe used alone, or two or more of them may be used in combination. Amongthem, PAN-based, pitch-based, and rayon-based carbon fibers, which areexcellent in specific strength and specific stiffness, are desirablyused in view of a weight reduction effect. Glass fibers are desirablyused in view of increasing the economy of the obtained structurematerial; carbon fibers and glass fibers are desirably used incombination in view of a balance between mechanical characteristics andeconomy in particular. Furthermore, aramid fibers are desirably used inview of increasing the impact absorption and shaping property of theobtained structure material; carbon fibers and aramid fibers aredesirably used in combination in view of a balance between mechanicalcharacteristics and impact absorption in particular. Reinforced fiberscoated with metal such as nickel, copper, or ytterbium can also be usedin view of increasing the conductivity of the obtained structurematerial. Among them, PAN-based carbon fibers, which are excellent instrength and mechanical characteristics such as modulus, are moredesirably used.

The reinforced fibers 3 are desirably discontinuous and dispersed in anearly monofilament form and in a random manner. The reinforced fibers 3are prepared in such a manner, whereby when a sheet-shaped structureprecursor or structure material is molded by applying external force,shaping into a complex shape is made easy. In addition, the reinforcedfibers 3 are prepared in such a manner, whereby voids formed by thereinforced fibers 3 become fine, and weak parts at fiber bundle ends ofthe reinforced fibers 3 in the structure material 1 can be minimized,and thus giving isotropy in addition to excellent reinforcing efficiencyand reliability. The nearly monofilament indicates that a reinforcedfiber single yarn is present as less than 500 fine-denier strands. Thereinforced fibers 3 are more desirably dispersed in a monofilament form.

Being dispersed in a nearly monofilament form or monofilament formindicates that, for a reinforced fiber 3 freely selected in thestructure material 1, the rate of single filaments having atwo-dimensional contact angle of 1° or more (hereinafter, also referredto as a fibers dispersed rate) is 80% or more or, in other words, that abundle in which two or more single filaments in the structure material 1are in contact with each other to be parallel to each other is less than20%. Consequently, the mass fraction of a fiber bundle with a filamentnumber of 100 or less at least in the reinforced fibers 3 particularlypreferably corresponds to 100%.

The two-dimensional contact angle refers to an angle formed by a singlefilament and a single filament being in contact with this singlefilament in the case of discontinuous reinforced fibers and is definedas an angle on an acute angle side within a range of 0° or more and 90°or less out of angles formed by the single filaments being in contactwith each other. The following further describes this two-dimensionalcontact angle with reference to a drawing. FIG. 2 is a schematic diagramof an example of a dispersion state of the reinforced fibers in afiber-reinforced mat when observed in a planar direction (FIG. 2(a)) anda thickness direction (FIG. 2(b)). With reference to a single filament11 a, the single filament 11 a is observed to cross single filaments 11b to 11 f in FIG. 2(a), whereas the single filament 11 a is not incontact with the single filaments 11 e and 11 f in FIG. 2(b). In thiscase, the single filaments 11 b to 11 d are objects for which thetwo-dimensional contact angle is evaluated for the single filament 11 aas the reference; the two-dimensional contact angle is an angle A on theacute angle side within a range of 0° or more and 90° or less out of thetwo angles formed by the two single filaments being in contact with eachother.

A method for measuring the two-dimensional contact angle is not limitedto a particular method; a method can be exemplified that observes theorientation of the reinforced fibers 3 from a surface of the structurematerial 1, for example. In this case, the surface of the structurematerial 1 is polished to expose the reinforced fibers 3, whereby thereinforced fibers 3 become easier to be observed. Another example thatcan be exemplified is a method that performs X-ray computed tomography(CT) transmission observation to take an orientation image of thereinforced fibers 3. For the reinforced fibers 3 having high X-raytransmissivity, fibers for a tracer are mixed into the reinforced fibers3, or a chemical for a tracer is applied to the reinforced fibers 3,whereby the reinforced fibers 3 become easier to be observed, which isthus desirable. When measurement is difficult by the methods, a methodcan be exemplified that puts the structure material 1 into ahigh-temperature environment such as an oven to burn off a resincomponent and then observes the orientation of the reinforced fibers 3from the reinforced fibers 3 that have been taken out using an opticalmicroscope or an electron microscope.

The fibers dispersed rate is measured by the following procedure basedon the method of observation described above. Specifically, thetwo-dimensional contact angle is measured for all the single filaments(the single filaments 11 b to 11 d in FIG. 2) being in contact with asingle filament selected at random (the signal filament 11 a in FIG. 2).This measurement is performed for 100 single filaments, and a rate iscalculated from the ratio of the number of signal filaments having atwo-dimensional contact angle of 1° or more to the total number of allthe single filaments for which the two-dimensional contact angle ismeasured.

Furthermore, the reinforced fibers 3 are particularly desirablydispersed in a random manner. The reinforced fibers 3 being dispersed ina random manner refers to the fact that the arithmetic mean of atwo-dimensional oriented angle of a reinforced fiber 3 freely selectedin the structure material 1 is within a range of 30° or more and 60° orless. The two-dimensional oriented angle refers to an angle formed by asingle filament of the reinforced fiber 3 and a single filament crossingthis single filament and is defined as an angle on an acute angle sidewithin a range of 0° or more and 90° or less out of angles formed by thesingle filaments crossing each other.

The following further describes this two-dimensional oriented angle withreference to a drawing. In FIGS. 2(a) and (b), with reference to thesingle filament 11 a, the single filament 11 a crosses the other singlefilaments 11 b to 11 f. The crossing means a state in which a singlefilament as a reference is observed to cross other single filaments on atwo-dimensional plane observed, does not necessarily require the singlefilament 11 a and the single filaments 11 b to 11 f to be in contactwith each other, and does not exclude a state in which the singlefilament 11 a is observed to cross the single filaments 11 b to 11 fwhen viewed in a projected manner. In other words, focusing on thesingle filament 11 a as the reference, all the single filaments 11 b to11 f are objects for which the two-dimensional oriented angle isevaluated; in FIG. 2(a), the two-dimensional oriented angle is the angleA on the acute angle side within a range of 0° or more and 90° or lessout of the two angles formed by the two crossing single filaments.

A method for measuring the two-dimensional oriented angle is not limitedto a particular method; a method can be exemplified that observes theorientation of the reinforced fibers 3 from a surface of the structureelement, for example, for which means similar to the method formeasuring the two-dimensional contact angle described above can beemployed. The mean of the two-dimensional oriented angle is measured bythe following procedure. Specifically, the mean of the two-dimensionaloriented angle is measured for all the single filaments (the singlefilaments 11 b to 11 f in FIG. 2) crossing a single filament selected atrandom (the signal filament 11 a in FIG. 2). When there are a largenumber of other single filaments crossing a single filament, forexample, an arithmetic mean measured by selecting 20 other crossingsingle filaments at random may be substituted. This measurement isrepeated a total of five times with reference to other single filaments,and its arithmetic mean is calculated as the arithmetic mean of thetwo-dimensional oriented angle.

The reinforced fibers 3 are dispersed in a nearly monofilament form andin a random manner, whereby the performance given by the reinforcedfibers 3 dispersed in a nearly monofilament form described above can beincreased to the maximum. In addition, isotropy can be imparted to themechanical characteristics of the structure material 1. In view of theforegoing, the fibers dispersed rate of the reinforced fibers 3 isdesirably 90% or more and more desirably closer to 100%. The arithmeticmean of the two-dimensional oriented angle of the reinforced fibers 3 isdesirably within a range of 40° or more and 50° or less and moredesirably closer to 45°, which is an ideal angle.

Examples of the reinforced fibers 3 not having a nonwoven fabric-likeform include a sheet substrate, a woven fabric substrate, and anon-crimped substrate in which the reinforced fibers 3 are arranged inone direction. These forms arrange the reinforced fibers 3 regularly anddensely, and thus there are few voids 4 in the structure material 1,which makes the impregnation of the resin 2 extremely difficult and mayform a non-impregnated part or significantly restrict alternatives aboutimpregnating means and/or resin type.

The form of the reinforced fibers 3 may be any of a continuousreinforced fiber having a length similar to that of the structurematerial 1 and a discontinuous reinforced fiber with a finite length cutinto a certain length; it is desirably a discontinuous reinforced fiberin view of easily impregnating the reinforced fibers 3 with the resin 2or being able to easily adjust the amount of the resin 2.

The volume content of the reinforced fibers 3 is within a range of 0.5%by volume or more and 55% by volume or less. When the volume content ofthe reinforced fibers 3 is less than 0.5% by volume, the reinforcingeffect caused by the reinforced fibers 3 is unable to be sufficient,which is thus undesirable. In contrast, when the volume content of thereinforced fibers 3 is larger than 55% by volume, the volume content ofthe resin 2 relative to the reinforced fibers 3 is relatively low, andit is unable to bind the reinforced fibers 3 within the structurematerial 1 together to make the reinforcing effect of the reinforcedfibers 3 sufficient and to satisfy the mechanical characteristicsespecially bending properties of the structure material 1, which is thusundesirable.

The reinforced fibers 3 are coated with the resin 2, in which thethickness of the resin 2 is preferably within a range of 1 μm or moreand 15 μm or less. As to the coated state of the reinforced fibers 3coated with the resin 2, coating at least intersection points of thesingle filaments of the reinforced fibers 3 contained in the structurematerial 1 is sufficient in view of the shape stability of the structurematerial 1 and the easiness and the degree of freedom in thicknesscontrol; as a more desirable manner, the resin 2 is desirably coatedaround the reinforced fibers 3 with the above thickness. This statemeans that the surface of the reinforced fibers 3 is not exposed owingto the resin 2 or, in other words, that the reinforced fibers 3 form anelectric wire-shaped coating by the resin 2. This formation furthercauses the structure material 1 to have shape stability and makes itsexpression of mechanical characteristics sufficient. In addition, thecoated state of the reinforced fibers 3 coated with the resin 2 is notrequired to be coated across the whole of the reinforced fibers 3 andmay be within a range in which the shape stability, the bending modulus,and the bending strength of the structure material 1 according to thepresent invention are not impaired.

The longer of the mass mean fiber length of the reinforced fibers 3 isdesirably within a range of 1 mm or more and 15 mm or less. With thislength, the reinforcing efficiency of the reinforced fibers 3 can beincreased, and thus excellent mechanical characteristics can be impartedto the structure material 1. When the longer of the mass mean fiberlength of the reinforced fibers 3 is less than 1 mm, the voids 4 withinthe structure material 1 are unable to be formed efficiently, and thespecific gravity may increase; in other words, it is difficult to obtainthe structure material 1 with a desired thickness even with the samemass, which is thus undesirable. In contrast, when the longer of themass mean fiber length of the reinforced fibers 3 is longer than 15 mm,the reinforced fibers 3 are likely to bend by their self-weight withinthe structure material 1 to cause the expression of mechanicalcharacteristics to be hindered, which is thus undesirable. The resincomponent of the structure material 1 is removed by a method such asburning or eluting, 400 remaining reinforced fibers 3 are selected atrandom, and the lengths thereof are measured down to 10 μm; the longerof the mass mean fiber length can be calculated as the mean lengththereof.

The voids 4 in the present invention each indicate a space formed by thereinforced fibers 3 coated with the resin 2 serving as columnar supportsand overlapping with each other or crossing each other. When a structureprecursor in which the reinforced fibers 3 are impregnated with theresin 2 in advance is heated to obtain a structure material, forexample, the melting or softening of the resin 2 along with heatingraises the reinforced fibers 3 to form the voids 4. This phenomenon isbased on the property of the reinforced fibers 3 inside the structureprecursor in a compressed state by pressurization rising by hair raisingforce caused by their modulus. The content of the voids 4 in thestructure material 1 is within a range of 10% by volume or more and 99%by volume or less. When the content of the voids 4 is less than 10% byvolume, the specific gravity of the structure material 1 is high, andlightness is not satisfied, which is thus undesirable. In contrast, whenthe content of the voids 4 is larger than 99% by volume or, in otherwords, the thickness of the resin 2 coated around the reinforced fibers3 is small, and the reinforcing of the reinforced fibers 3 in thestructure material 1 is not performed sufficiently to decreasemechanical characteristics, which is thus undesirable. The upper limitof the content of the voids 4 is desirably 97% by volume. In the presentinvention, as to the volume content, the sum of the respective volumecontents of the resin 2, the reinforced fibers 3, and the voids 4included in the structure material 1 is defined as 100% by volume.

A thickness St of the structure material 1 satisfies a conditionalexpression St≥Lf²·(1−cos(θf)) where the length of the reinforced fibers3 is Lf and the oriented angle of the reinforced fibers 3 in a sectionaldirection of the structure material 1 is θf. The thickness St of thestructure material 1 not satisfying the conditional expression indicatesthat the reinforced fibers 3 in the structure material 1 are bending orthat a balance between the structure material 1 with a desired thicknessand a fiber length is poor. This indicates that the structure material 1is poor in the degree of freedom in thickness design because the featureof the charged reinforced fibers 3 is unable to be sufficientlyexpressed, and furthermore, as to characteristics using the tensilestrength and the tensile modulus of the reinforced fibers 3 among themechanical characteristics of the structure material 1, an efficientreinforcing effect is unable to be obtained because the straightness ofthe reinforced fibers 3 is lost, which is thus undesirable. In theconditional expression, the value is preferably within a range of 2% ormore and 20% or less of the thickness St of the structure material 1 andparticularly preferably within a range of 5% or more and 18% or lessthereof considering that a balance can be obtained between bendingmodulus and specific bending modulus as the characteristics of thestructure material 1 formed by the length and the oriented angle of thereinforced fibers 3 and that owing to the fiber length and its orientedangle in the structure material 1, deformation in a state beforesolidification or curing during a molding process is easily performed tofacilitate the molding of the desired structure material 1. The unitsused for the conditional expression are St [mm], Lf [mm], and θf [°].

The length Lf of the reinforced fibers 3 can be calculated as the longerof the mass mean fiber length calculated from the lengths obtained byremoving the resin component of the structure material 1 by a methodsuch as burning or eluting, selecting 400 remaining reinforced fibers 3at random, and measuring the lengths thereof down to 10 μm. The orientedangle θf of the reinforced fibers 3 in the sectional direction of thestructure material 1 is the degree of inclination relative to thesectional direction of the structure material 1 or, in other words, thedegree of inclination of the reinforced fibers 3 relative to thethickness direction. A larger value indicates that the reinforced fibers3 are inclined in an upright manner in the thickness direction, and thevalue is given within a range of 0° or more and 90° or less. In otherwords, the oriented angle θf of the reinforced fibers 3 is set to bewithin the range, whereby reinforcing function in the structure material1 can be expressed more effectively. The upper limit of the orientedangle θf of the reinforced fibers 3, which is not limited to aparticular value, is desirably 60° or less and more desirably 45° orless in view of the expression of bending modulus as the structurematerial 1. When the oriented angle θf of the reinforced fibers 3 isless than 3°, the reinforced fibers 3 in the structure material 1 areoriented in a planar manner or, in other words, a two-dimensionalmanner, and the degree of freedom in the thickness of the structurematerial 1 decreases, and lightness is unable to be satisfied, which isthus undesirable. For this reason, the oriented angle θf of thereinforced fibers 3 is preferably 3° or more.

The oriented angle θf of the reinforced fibers 3 can be measured basedon observation of a perpendicular section relative to the planardirection of the structure material 1. FIG. 3 is a schematic diagram ofan example of sectional structures in the planar direction (FIG. 3(a))and the thickness direction (FIG. 3(b)) of the structure materialaccording to the first and second modes of the present invention. InFIG. 3(a), the sections of reinforced fibers 3 a and 3 b areapproximated to an oval shape in order to simplify measurement. In thesection of the reinforced fiber 3 a, its aspect ratio of the oval (=ovalmajor axis/oval minor axis) is viewed to be smaller, whereas in thesection of the reinforced fiber 3 b, its aspect ratio of the oval isviewed to be larger. Meanwhile, according to FIG. 3(b), the reinforcedfiber 3 a has an inclination nearly parallel relative to a thicknessdirection Y, whereas the reinforced fiber 3 b has a certain amount ofinclination relative to the thickness direction Y. In this case, as tothe reinforced fiber 3 b, an angle θx formed by a planar direction X ofthe structure material 1 and a fiber principal axis (the major axialdirection in the oval) a is nearly equal to an out-of-plane angle θf ofthe reinforced fiber 3 b. In contrast, as to the reinforced fiber 3 a,there is a large deviation between the angle θx and the oriented angleθf, and it cannot be said that the angle θx is reflective of theoriented angle θf. Consequently, when the oriented angle θf is read fromthe perpendicular section relative to the planar direction of thestructure material 1, the aspect ratio of the oval of a fiber sectionhaving a certain value or more is extracted, whereby the accuracy ofdetecting the oriented angle θf can be increased.

For an indicator of the aspect ratio of the oval to be extracted, amethod can be employed that when the sectional shape of the singlefilament is close to a perfect circle or, that is, when a fiber aspectratio in a section perpendicular to the longitudinal direction of thereinforced fibers 3 is 1.1 or less, the angle θx formed by the planardirection X and the fiber principal axis α is measured for thereinforced fibers 3 having an aspect ratio of the oval of 20 or more,and this angle is employed as the oriented angle θf. In contrast, whenthe sectional shape of the single filament is an oval shape, a cocoonshape or the like, in which the fiber aspect ratio is larger than 1.1,it is better to focus on the reinforced fibers 3 having a larger aspectratio of the oval to measure the oriented angle θf; the reinforcedfibers 3 having an aspect ratio of the oval of 30 or more when the fiberaspect ratio is 1.1 or more and less than 1.8, having an aspect ratio ofthe oval of 40 or more when the fiber aspect ratio is 1.8 or more andless than 2.5, and having an aspect ratio of the oval of 50 or more whenthe fiber aspect ratio is 2.5 or more may be selected, and the orientedangle θf thereof may be measured.

The specific bending modulus of the structure material 1 represented asEc^(1/3)·ρ⁻¹ is within a range of 3 or more and 20 or less where thebending modulus of the structure material 1 is Ec and the specificgravity of the structure material 1 is ρ. When the specific bendingmodulus of the structure material 1 is less than 3, even if the bendingmodulus is high, the specific gravity is also high, and a desired weightreduction effect is unable to be obtained, which is thus undesirable. Incontrast, when the specific bending modulus of the structure material 1is larger than 20, it is indicated that the bending modulus is low,although the weight reduction effect is sufficient; it is difficult tomaintain a shape desired as the structure material 1, and the bendingmodulus of the structure material 1 itself is poor, which is thusundesirable. The specific bending modulus of steel materials andaluminum is 1.5 or less in general; the region of the specific bendingmodulus extremely excellent compared with these metallic materials isachieved. Furthermore, the specific bending modulus of the structurematerial 1 is 3 or more exceeding 2.3, which is a general specificbending modulus of carbon fiber-reinforced plastic composite materialsattracting attention for their weight reduction effect, and furtherdesirably 5 or more.

The bending modulus Ec of the structure material 1 may be 3 GPa or moreand desirably 6 GPa or more. When the bending modulus Ec of thestructure material 1 is less than 3 GPa, the range of use as thestructure material 1 is limited, which is thus undesirable. In addition,to facilitate the design of the structure material 1, the bendingmodulus desirably has isotropy. The upper limit of the bending modulusis not limited; in a structure material formed of reinforced fibers anda resin in general, a value calculated from the respective moduli of thereinforced fibers and the resin as its components can be the upperlimit. In the structure material according to the present invention,both when the structure material is used alone and when it is used incombination with another member, a member is designed using the bendingmodulus of the structure material itself; 5 GPa is enough for practicaluse.

The specific gravity ρ of the structure material 1 is desirably 0.9g/cm³ or less. When the specific gravity ρ of the structure material 1is larger than 0.9 g/cm³, that means that mass as the structure material1 increases, resulting in an increase in mass when being made into aproduct, which is thus undesirable. The lower limit of the specificgravity is not limited; in a structure material formed of reinforcedfibers and a resin in general, a value calculated from the respectivevolume ratios of the reinforced fibers, the resin, and the voids as itscomponents can be the lower limit. In the structure material accordingto the present invention, both when the structure material is used aloneand when it is used in combination with another member, the specificgravity of the structure material itself is desirably 0.03 g/cm³ or morein view of maintaining the mechanical characteristics of the structurematerial, although it varies depending on the reinforced fibers and theresin used.

The porosity of parts within 30% to a midpoint position in the thicknessdirection from surfaces of the structure material 1 is desirably withina range of 0% by volume or more and less than 10% by volume, and theporosity of a residual part is desirably within a range of 10% by volumeor more and 99% by volume or less. A smaller porosity gives excellencein mechanical characteristics, whereas a larger porosity givesexcellence in lightness. In other words, when the structure material 1is formed of a material of the same composition, the porosity of theparts within 30% to the midpoint position in the thickness directionfrom the surfaces of the structure material 1 is 0% by volume or moreand less than 10% by volume, thereby ensuring the mechanicalcharacteristics of the structure material 1, and the porosity of theresidual part is within a range of 10% by volume or more and 99% byvolume or less, thereby satisfying lightness, which is thus desirable.

The thickness of the structure material 1 in the present invention canbe determined by the shortest distance connecting one point on a surfaceand a surface on the back thereof for which the thickness is desired tobe determined. The midpoint in the thickness direction means anintermediate point in the thickness of the structure material 1. Theparts within 30% to the midpoint position in the thickness directionfrom the surfaces of the structure material means parts containing up to30% distance from the surfaces of the structure material 1 when thedistance from the surfaces of the structure material 1 to its midpointin the thickness direction is 100%. The residual part means a residualpart after removing a part within 30% to the midpoint position in thethickness direction from one surface of the structure material 1 and apart within 30% to the midpoint position in the thickness direction fromthe other surface. Parts R1 within 30% to the midpoint position in thethickness direction from the surfaces of the structure material 1 and aresidual part R2 may be present at different positions in the thicknessdirection of the structure material 1 as illustrated in FIG. 4 orpresent at different positions in the planar direction thereof asillustrated in FIG. 5.

The reinforced fibers 3 in the present invention desirably have anonwoven fabric-like form in view of the easiness of the impregnation ofthe resin 2 into the reinforced fibers 3. Furthermore, the reinforcedfibers 3 have a nonwoven fabric-like form, whereby in addition to easyhandleability of the nonwoven fabric itself, impregnation can be madeeasy even in the case of thermoplastic resins, which are generally highin viscosity, which is thus desirable. The nonwoven fabric-like shapeindicates a form in which strands and/or monofilaments of the reinforcedfibers 3 are dispersed irregularly in a planar form; examples thereofinclude a chopped strand mat, a continuous strand mat, a paper-makingmat, a carding mat, and an air-laid mat (hereinafter, referred tocollectively as a fiber-reinforced mat).

Examples of a method for manufacturing the fiber-reinforced mat includedin the structure material 1 include a method for manufacturing thefiber-reinforced mat by dispersing the reinforced fibers 3 in a strandand/or a nearly monofilament form in advance. Examples of the method formanufacturing the fiber-reinforced mat include a dry process such as anair-laid method that disperses the reinforced fibers 3 to form a sheetwith an airflow and a carding method that shapes the reinforced fibers 3while mechanically carding them to form a sheet and a wet process byRadright method that stirs the reinforced fibers 3 in the water to makepaper as known techniques. Examples of means for making the reinforcedfibers 3 closer to a monofilament form include in the dry process amethod that provides fiber-opening bars, a method that vibratesfiber-opening bars, a method that makes meshes of a card finer, and amethod that adjusts the rotational speed of a card. Examples thereofinclude in the wet process a method that adjusts the stirring conditionof the reinforced fibers 3, a method that dilutes a reinforced fiberconcentration of a dispersion, a method that adjusts the viscosity of adispersion, and a method that inhibits an eddy when a dispersion istransferred. In particular, the fiber-reinforced mat is desirablymanufactured by the wet process, and the concentration of charged fibersis increased or the flow rate (flow) of a dispersion and the speed of amesh conveyor are adjusted, whereby the rate of the reinforced fibers 3in the fiber-reinforced mat can be easily adjusted. The speed of themesh conveyor is decreased relative to the flow rate of the dispersion,whereby the orientation of fibers in an obtained fiber-reinforced mat isdifficult to be directed to a taking direction, and a bulkyfiber-reinforced mat can be manufactured, for example. Thefiber-reinforced mat may be formed of the reinforced fibers 3 alone. Thereinforced fibers 3 may be mixed with a matrix resin component in apowdery form or a fibrous form. The reinforced fibers 3 may be mixedwith organic compounds or inorganic compounds. The reinforced fibers 3may be bonded to each other with a resin component.

Furthermore, the fiber-reinforced mat may be impregnated with the resin2 in advance to form a structure precursor. For a method formanufacturing the structure precursor according to the presentinvention, a method that applies pressure to the fiber-reinforced matwith the resin 2 being in a state heated at a temperature melting orsoftening or more to impregnate the fiber-reinforced mat therewith isdesirably used in view of the easiness of manufacture. Specifically, amethod that melt-impregnates the fiber-reinforced mat with a laminatearranging the resin 2 from both sides in the thickness direction can bedesirably exemplified.

For equipment for implementing the methods, a compression moldingmachine or a double belt press can be suitably used. The former is for abatch type; an intermittent type press system arranging two or moremachines for heating and cooling in a row can improve productivity. Thelatter is for a continuous type, which can easily perform continuousprocessing and is thus excellent in continuous productivity.

In manufacturing the structure material 1 according to the presentinvention, a method that manufactures it by at least the followingprocesses [1] and [2] is preferably employed in view of the easiness ofmanufacture.

Process [1]: a process for applying pressure with the resin 2 heated ata temperature melting or softening or more and impregnating thefiber-reinforced mat with the resin 2 to prepare a structure precursor

Process [2]: a process for performing thickness adjustment with thestructure precursor heated to swell it

Process [2] is a process for performing thickness adjustment with thestructure precursor obtained at Process [1] heated to swell it. Thetemperature heated in this process preferably gives an amount of heatsufficient for melting or softening the resin 2 when the resin 2included in the structure material 1 is a thermoplastic resin in view ofthe thickness control and the manufacturing speed of the structurematerial 1 to be manufactured;

-   -   specifically, a temperature that is higher than a melting        temperature by 10° C. or more and is the thermal decomposition        temperature of the thermoplastic resin or less is preferably        given. When a thermosetting resin is used as the resin 2, an        amount of heat sufficient for melting or softening a        thermosetting resin raw material before it forms a crosslinked        to be cured is preferably given in view of the thickness control        and the manufacturing speed of the structure material 1 to be        manufactured.

A method for performing thickness control is not limited to a particularmethod so long as it can control the heated structure precursor to be atarget thickness; a method that restricts the thickness using metallicplates or the like and a method that performs thickness control bypressure given to the structure precursor are exemplified in view of theeasiness of manufacture. For equipment for implementing the methods, acompression molding machine or a double belt press can be suitably used.The former is for a batch type; an intermittent type press systemarranging two or more machines for heating and cooling in a row canimprove productivity. The latter is for a continuous type, which caneasily perform continuous processing and is thus excellent in continuousproductivity.

Examples of the fiber-reinforced mat not having a nonwoven fabric-likeform include a sheet substrate, a woven fabric substrate, and anon-crimped substrate in which the reinforced fibers 3 are arranged inone direction. These forms arrange the reinforced fibers 3 regularly anddensely, and thus there are few voids in the fiber-reinforced mat, andthe thermoplastic resin does not form a sufficient anchoring structure,and thus when it is made into a core forming layer, bonding abilitydecreases. In addition, when the resin 2 is a thermoplastic resin,impregnation is extremely difficult, which forms a non-impregnated partor significantly restricts alternatives about impregnating means orresin type.

In the present invention, to the extent that the features of the presentinvention are not impaired, a sandwich structure using the structurematerial 1 or the structure precursor as a core layer and using anintermediate sheet material in which the reinforced fibers 3 in acontinuous form are impregnated with a resin as a skin layer is alsofeasible. The reinforced fibers 3 in a continuous form are continuouswith a length of 100 mm or more at least in one direction; many arearranged in one direction to form an aggregate, or what is called areinforced fiber bundle, which is continuous across the entire length ofthe sandwich structure. Examples of the form of the intermediate sheetmaterial formed of the reinforced fibers 3 in a continuous form includea woven fabric including reinforced fiber bundles formed of manyreinforced fibers 3 in a continuous form, a reinforced fiber bundle inwhich many reinforced fibers 3 in a continuous form are arranged in onedirection (a unidirectional fiber bundle), and a unidirectional wovenfabric including this unidirectional fiber bundle. The reinforced fibers3 may include a plurality of fiber bundles of the same form or include aplurality of fiber bundles of different forms. The number of thereinforced fibers included in one reinforced fiber bundle is normally300 to 48,000; in view of the manufacture of prepregs and themanufacture of woven fabrics, the number is desirably 300 to 24,000 andmore desirably 1,000 to 12,000.

To control the bending modulus, lamination with the direction of thereinforced fibers 3 changed is desirably used. In particular, inefficiently increasing the modulus and strength of the sandwichstructure, a continuous reinforced fiber with fiber bundles aligned inone direction (referred to as UD) is desirably used.

Examples of the structure material 1 include electric and electronicdevice parts such as “housings, trays, chassis, interior members, andcases of personal computers, displays, office automation (OA) devices,cellular phones, mobile information terminals, personal digitalassistants (PDAs) (mobile information terminals such as electronicnotepads), video cameras, optical devices, audio devices, airconditioners, lighting devices, entertainment goods, toy goods, andother home appliances”; “various kinds of members, various kinds offrames, various kinds of hinges, various kinds of arms, various kinds ofwheel axles, various kinds of bearings for wheels, and various kinds ofbeams”; “outer plates and body parts such as hoods, roofs, doors,fenders, trunk lids, side panels, rear end panels, front bodies, underbodies, various kinds of pillars, various kinds of members, variouskinds of frames, various kinds of beams, various kinds of supports,various kinds of rails, and various kinds of hinges”; “exterior partssuch as bumpers, bumper beams, moldings, under covers, engine covers,current plates, spoilers, cowl louvers, and aerodynamic parts”;“interior parts such as instrument panels, seat frames, door trims,pillar trims, steering wheels, and various kinds of modules”; structureparts for automobiles and two-wheeled vehicles such as “motor parts,compressed natural gas (CNG) tanks, and gasoline tanks”; parts forautomobiles and two-wheeled vehicles such as “battery trays, headlampsupports, pedal housings, protectors, lamp reflectors, lamp housings,noise shields, and spare tire covers”; building materials such as “wallmembers such as sound insulation walls and soundproofing walls”; andparts for aircraft such as “landing gear pods, winglets, spoilers,edges, rudders, elevators, fairings, ribs, and seats”. In view ofmechanical characteristics, the structure material 1 is desirably usedfor automobile interior and exterior, electric and electronic devicehousings, bicycles, structure materials for sporting goods, aircraftinterior materials, boxes for transportation, and building materials.Among them, the structure material 1 is suitable for module membersincluding a plurality of parts in particular.

EXAMPLES

The following describes the present invention in more detail withreference to examples.

(1) Volume Content Vf of Reinforced Fibers in Structure Material

After a mass Ws of a structure material was measured, the structurematerial was heated at 500° C. for 30 minutes in the air to burn off aresin component, a mass Wf of remaining reinforced fibers was measured,and a volume content Vf was calculated by the following expression.

Vf (% by volume)=(Wf/ρf)/{Wf/ρf+(Ws−Wf)/pr}×100

ρf: the density of the reinforced fibers (g/cm³)ρr: the density of the resin (g/cm³)

(2) Bending Test on Structure Material

Test pieces were cut out of the structure material, and the bendingmodulus thereof was measured in accordance with ISO 178 Method (1993).As to the test pieces, test pieces cut out in four directions includinga 0° direction freely set and +45°, −45°, and 90° directions wereprepared. The number of measurement n=5 was set for each of thedirections, and its arithmetic mean was defined as a bending modulus Ec.As to a measurement apparatus, “INSTRON” (registered trademark) model5565 universal material testing system (manufactured by INSTRON JAPANCo., Ltd.) was used. From the obtained result, the specific bendingmodulus of the structure material was calculated by the followingexpression.

Specific bending modulus=Ec ^(1/3)/ρ

(3) Oriented Angle θf of Reinforced Fibers of Structure Material

A piece with a width of 25 mm was cut out of the structure material, wasembedded in an epoxy resin and was polished so as to cause aperpendicular section in a sheet thickness direction to be a surface tobe observed to prepare a sample. The sample was magnified 400 times witha laser microscope (VK-9510 manufactured by KEYENCE CORPORATION) toobserve a fiber sectional shape. An observed image was developed ontomulti-purpose image analysis software, an individual fiber sectionviewed in the observation image was extracted using a computer programincorporated in the software, an oval inscribed in the fiber section wasprovided, and the shape of the fiber section was approximated thereto(hereinafter, referred to as a fiber oval). Furthermore, for a fiberoval with an aspect ratio, which is represented by a major axial lengthα/a minor axial length β of the fiber oval, of 20 or more, an angleformed by the planar direction X and a major axial direction of thefiber oval was determined. The operation was repeated for samples to beobserved extracted from different parts of the structure material,whereby oriented angles were measured for a total of 600 reinforcedfibers, and their arithmetic mean was determined to be the orientedangle θf of the reinforced fibers.

(4) Specific Gravity ρ of Structure Material

A test piece was cut out of the structure material, and an apparentspecific gravity of the structure material was measured with referenceto JIS K7222 (2005). The dimensions of the test piece were 100 mm longand 100 mm wide. The length, width, and thickness of the test piece weremeasured with a micrometer, and a volume V of the test pieces wascalculated from the obtained values. A mass M of the cut-out test piecewas measured with an electronic balance. The obtained mass M and volumeV were substituted into the following expression to calculate a specificgravity ρ of the structure material.

ρ[g/cm³]=10³ ×M[g]/V[mm³]

(5) Volume Content of Voids of Structure Material

A test piece of 10 mm long and 10 mm wide was cut out of the structurematerial, and a section was observed with a scanning electron microscope(SEM) (model S-4800 manufactured by Hitachi High-TechnologiesCorporation) to photograph ten sites at regular intervals from thesurface of the structure material with a 1,000-fold magnification. Foreach image, an area A_(a) of voids within the image was determined.Furthermore, the area A_(a) of the voids was divided by the area of theentire image to calculate a porosity. The volume content of the voids ofthe structure material was determined by an arithmetic mean from theporosity at a total of 50 sites photographed at ten sites each for fivetest pieces. In the structure material, to determine a case when theporosity of a part to the midpoint position in the thickness directionfrom the surface and the porosity of the residual part are differentfrom each other, the volume content of voids was calculated for each ofthe ten sites photographed at regular intervals, and the volume contentof voids within a range of 0% by volume or more and less than 10% byvolume and the volume content of voids within a range of 10% by volumeor more and 99% by volume or less were separately determined.

(6) Thickness of Resin with which Reinforced Fibers are Coated

A test piece of 10 mm long and 10 mm wide was cut out of the structurematerial, and a section was observed with a scanning electron microscope(SEM) (model S-4800 manufactured by Hitachi High-TechnologiesCorporation) to photograph ten sites freely selected with a 3,000-foldmagnification. From 50 sites freely selected in which sections of thereinforced fibers were cut in an obtained image, a coating thickness ofthe resin with which the reinforced fibers were coated was measured. Forthe thickness of the resin with which the reinforced fibers were coated,the arithmetic mean of the measurement results at the 50 sites was used.

[Carbon Fiber 1]

A copolymer with polyacrylonitrile as a main component was subjected tospun processing, calcined processing, and surface oxidation treatmentprocessing to obtain a continuous carbon fiber with a total single yarnnumber of 12,000. The characteristics of this continuous carbon fiberwere as follows.

Single filament diameter: 7 μm

Specific gravity: 1.8Tensile strength: 4,600 MPaTensile modulus: 220 GPa

[Carbon Fiber 2]

A copolymer with polyacrylonitrile as a main component was subjected tospun processing, calcined processing, and surface oxidation treatmentprocessing to obtain a continuous carbon fiber with a total single yarnnumber of 12,000. The characteristics of this continuous carbon fiberwere as follows.

Single filament diameter: 7 μm

Specific gravity: 1.8Tensile strength: 4,100 MPaTensile modulus: 420 GPa

[PP Resin]

A resin sheet with a weight per unit area of 100 g/m² formed of 80% bymass of an unmodified polypropylene resin (“Prime Polypro” (registeredtrademark) J105G manufactured by PRIME POLYMER Co, Ltd.) and 20% by massof an acid-modified polypropylene resin (“ADMER” QB510 manufactured byMitsui Chemicals, Inc.) was prepared. Table 1 lists the characteristicsof the obtained resin sheet.

[PA Resin]

A resin film with a weight per unit area of 124 g/m² formed of a nylon 6resin (“AMILAN” (registered trademark) CM1021T manufactured by TorayIndustries, Inc.) was prepared. Table 1 lists the characteristics of theobtained resin film.

[PC Resin]

A resin film with a weight per unit area of 132 g/m² formed of apolycarbonate resin (“lupilon” (registered trademark) H-4000manufactured by Mitsubishi Engineering-Plastics Corporation) wasprepared. Table 1 lists the characteristics of the obtained resin film.

[PPS Resin]

A resin nonwoven fabric with a weight per unit area of 147 g/m² formedof a polyphenylene sulfide resin (“TORELINA” (registered trademark)M2888 manufactured by Toray Industries, Inc.) was prepared. Table 1lists the characteristics of the obtained resin nonwoven fabric.

[Epoxy Resin]

Blended were 40 parts by mass of “Epototo” YD128 (manufactured by TohtoKasei Co., Ltd.), 20 parts by mass of “Epototo” YD128G (manufactured byTohto Kasei Co., Ltd.), 20 parts by mass of “Epo Tohto” 1001(manufactured by Japan Epoxy Resins Co., Ltd.), and 20 parts by mass of“Epo Tohto” 1009 (manufactured by Japan Epoxy Resins Co., Ltd.) as epoxyresins; 4 parts by mass of DICY 7 (dicyandiamide manufactured by JapanEpoxy Resins Co., Ltd.) and 3 parts by mass of DCMU 99(3-(3,4-dichlorophenyl)-1,1-dimethylurea manufactured by HODOGAYACHEMICAL CO., LTD.) as curing agents; and 5 parts by mass of “Vinylec” K(polyvinyl formal manufactured by CHISSO CORPORATION) as an additive.From this blend, a resin film with a weight per unit area of 132 g/m²was prepared using a knife coater. Table 1 lists the characteristics ofthe obtained resin film.

[Fiber-Reinforced Mat 1]

Carbon Fiber 1 was cut into a length of 5 mm to obtain chopped carbonfibers. The chopped carbon fibers were charged into a cotton opener toobtain a cotton-like reinforced fiber aggregate in which almost noreinforced fiber bundle with an original thickness is present. Thisreinforced fiber aggregate was charged into a carding device having acylinder roll with a diameter of 600 mm to form a sheet-shaped webformed of reinforced fibers. In this process, the number of revolutionsof the cylinder roll was 320 rpm, and the speed of a doffer was 13m/min. This web was stacked to obtain Fiber-Reinforced Mat 1. Table 2lists the characteristics of the obtained Fiber-Reinforced Mat 1.

[Fiber-Reinforced Mat 2]

Carbon Fiber 1 was cut into 3 mm with a strand cutter to obtain choppedcarbon fibers. A dispersion with a concentration of 0.1% by masscontaining water and a surfactant (polyoxyethylene lauryl ether (productname) manufactured by nacalai tesque) was prepared. Using thisdispersion and the chopped carbon fibers, a fiber-reinforced mat wasmanufactured using an apparatus for manufacturing a fiber-reinforced matillustrated in FIG. 6. The manufacturing apparatus illustrated in FIG. 6includes a cylindrical vessel with a diameter of 1,000 mm having anopening cock at the lower part of the vessel as a dispersing tank and alinear transportation unit (an inclination angle of 30°) connecting thedispersing tank and a paper-making tank. A stirrer is attached to anopening at the top face of the dispersing tank. The chopped carbonfibers and the dispersion (a dispersing medium) can be charged from theopening. The paper-making tank is a tank including a mesh conveyorhaving a paper-making face with a width of 500 mm on its bottom, and aconveyor that can convey a carbon fiber substrate (a paper-makingsubstrate) is connected to the mesh conveyor. Paper making was performedwith a carbon fiber concentration in the dispersion of 0.05% by mass.The carbon fiber substrate after paper making was dried for 30 minutesin a drying oven at 200° C. to obtain Fiber-Reinforced Mat 2. Theobtained weight per unit area was 50 g/m². Table 2 lists thecharacteristics of the obtained Fiber-Reinforced Mat 2.

[Fiber-Reinforced Mat 3]

Fiber-Reinforced Mat 3 was obtained in a manner similar toFiber-Reinforced Mat 2 except that Carbon Fiber 1 was cut into 6 mm witha strand cutter to obtain chopped carbon fibers. Table 2 lists thecharacteristics of the obtained Fiber-Reinforced Mat 3.

[Fiber-Reinforced Mat 4]

Fiber-Reinforced Mat 4 was obtained in a manner similar toFiber-Reinforced Mat 2 except that Carbon Fiber 1 was cut into 12 mmwith a strand cutter to obtain chopped carbon fibers. Table 2 lists thecharacteristics of the obtained Fiber-Reinforced Mat 4.

[Fiber-Reinforced Mat 5]

Carbon Fiber 1 was cut into 25 mm with a strand cutter to obtain choppedcarbon fibers. The obtained chopped carbon fibers were caused to fallfreely from a height of 80 cm to obtain Fiber-Reinforced Mat 5 in whichthe chopped carbon fibers were randomly distributed. Table 2 lists thecharacteristics of the obtained Fiber-Reinforced Mat 5.

[Fiber-Reinforced Mat 6]

Fiber-Reinforced Mat 6 was obtained in a manner similar toFiber-Reinforced Mat 2 except that Carbon Fiber 2 was cut into 6 mm witha strand cutter to obtain chopped carbon fibers. Table 2 lists thecharacteristics of the obtained Fiber-Reinforced Mat 6.

TABLE 1 PP resin PA resin PC resin PPS resin Epoxy resin Type —Polypropylene Nylon 6 Polycarbonate Polyphenylene Epoxy sulfide Weightper unit area g/m² 100 124 132 147 132 Specific gravity g/m³ 0.92 1.131.20 1.34 1.20 Melting point ° C. 165 225 — 280 — Softening point ° C. —— 150 — — Decomposition ° C. 298 338 424 463 250 starting temperature

TABLE 2 Fiber-Reinforced Fiber-Reinforced Fiber-ReinforcedFiber-Reinforced Fiber-Reinforced Fiber-Reinforced Mat 1 Mat 2 Mat 3 Mat4 Mat 5 Mat 6 Mat form — Dry web Wet web Wet web Wet web Chopped strandWet web mat Nonwoven fabric Nonwoven fabric Nonwoven fabric Nonwovenfabric Nonwoven fabric Nonwoven fabric Dispersion — Nearly MonofilamentMonofilament Monofilament Strand (bundle Monofilament state ofmonofilament of 12,000) reinforced fibers Fiber type — Carbon Fiber 1Carbon Fiber 1 Carbon Fiber 1 Carbon Fiber 1 Carbon Fiber 1 Carbon Fiber2 Fiber length mm 5 3 6 12 25 6 (Lf) Weight per unit g/m² 50 50 50 50 5050 area of fiber- reinforced mat

First Example

A laminate was prepared in which Fiber-Reinforced Mat 3 as afiber-reinforced mat and the PP resin as a resin sheet were arranged inorder of [resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet]. Subsequently, a structure material was obtained through thefollowing processes (I) through (V). In the obtained structure material,voids with the reinforced fibers as columnar supports were found bysectional observation. Table 3 lists the characteristics of the obtainedstructure material.

(I) The laminate is arranged within a mold cavity for press moldingpreheated at 230° C., and the mold is closed.

(II) Subsequently, after being maintained for 120 seconds, the mold ismaintained for additional 60 seconds with a pressure of 3 MPa applied.

(III) After Process (II), the mold cavity is opened, and a metallicspacer is inserted into the end thereof to perform adjustment to give athickness of 3.4 mm when the structure material is obtained.

(IV) Subsequently, the mold cavity is again fastened, and the cavitytemperature is decreased to 50° C. with the pressure maintained.

(V) The mold is opened, and the structure material is taken out of it.

Second Example

A structure material was obtained in a manner similar to the firstexample except that a laminate was prepared in which Fiber-ReinforcedMat 3 as a fiber-reinforced mat and the PP resin as a resin sheet werearranged in order of [resin sheet/fiber-reinforced mat/resinsheet/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet/fiber-reinforced mat/fiber-reinforced mat/resinsheet/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet/fiber-reinforced mat/resin sheet]. Table 3 lists thecharacteristics of the obtained structure material.

Third Example

A structure material was obtained in a manner similar to the firstexample except that a laminate was prepared in which Fiber-ReinforcedMat 3 as a fiber-reinforced mat and the PP resin as a resin sheet werearranged in order of [resin sheet/fiber-reinforced mat/resinsheet/fiber-reinforced mat/fiber-reinforced mat/resinsheet/fiber-reinforced mat/resin sheet] and that the thickness of themetallic spacer at Process (III) was changed from 3.4 mm to 5.6 mm.Table 3 lists the characteristics of the obtained structure material.

Fourth Example

A structure material was obtained in a manner similar to the firstexample except that the resin sheet was changed from the PP resin to thePA resin, that the preheating temperature at Process (I) was changedfrom 230° C. to 260° C., that the cavity temperature at Process (IV) waschanged from 50° C. to 60° C., and that the thickness of the metallicspacer at Process (III) was changed from 3.4 mm to 3.3 mm. Table 3 liststhe characteristics of the obtained structure material.

Fifth Example

A structure material was obtained in a manner similar to the firstexample except that the resin sheet was changed from the PP resin to thePPS resin, that the preheating temperature at Process (I) was changedfrom 230° C. to 300° C., that the cavity temperature at Process (IV) waschanged from 50° C. to 150° C., and that the thickness of the metallicspacer at Process (III) was changed from 3.4 mm to 2.9 mm. Table 3 liststhe characteristics of the obtained structure material.

Sixth Example

A structure material was obtained in a manner similar to the firstexample except that the resin sheet was changed from the PP resin to thePC resin, that the preheating temperature at Process (I) was changedfrom 230° C. to 300° C., and that the cavity temperature at Process (IV)was changed from 50° C. to 80° C. Table 3 lists the characteristics ofthe obtained structure material.

Seventh Example

A structure material was obtained in a manner similar to the firstexample except that the fiber-reinforced mat was changed fromFiber-Reinforced Mat 3 to Fiber-Reinforced Mat 6. Table 3 lists thecharacteristics of the obtained structure material.

Eighth Example

A laminate was obtained in a manner similar to the first example withthe resin sheet changed from the PP resin to the epoxy resin.Subsequently, a structure material was obtained through the followingprocesses (I) through (V). In the obtained structure material, voidswith the reinforced fibers as columnar supports were found by sectionalobservation. Table 3 lists the characteristics of the obtained structurematerial.

(I) The laminate is arranged within a mold cavity for press moldingpreheated at 150° C., and the mold is closed.

(II) Subsequently, the mold is maintained for additional 20 seconds witha pressure of 3 MPa applied.

(III) After Process (II), the mold cavity is opened, and a metallicspacer is inserted into the end thereof to perform adjustment to give athickness of 3.3 mm when the structure material is obtained.

(IV) Subsequently, the mold cavity is again fastened, and the cavitytemperature is decreased to 30° C. with the pressure maintained.

(V) The mold is opened, and the structure material is taken out of it.

Ninth Example

A structure material was obtained in a manner similar to the firstexample except that the fiber-reinforced mat was changed fromFiber-Reinforced Mat 3 to Fiber-Reinforced Mat 2. Table 3 lists thecharacteristics of the obtained structure material.

Tenth Example

A structure material was obtained in a manner similar to the firstexample except that the fiber-reinforced mat was changed fromFiber-Reinforced Mat 3 to Fiber-Reinforced Mat 4. Table 3 lists thecharacteristics of the obtained structure material.

Eleventh Example

A structure material was obtained in a manner similar to the firstexample except that the fiber-reinforced mat was changed fromFiber-Reinforced Mat 3 to Fiber-Reinforced Mat 1. Table 3 lists thecharacteristics of the obtained structure material.

Twelfth Example

A structure material was obtained in a manner similar to the firstexample except that the thickness of the metallic spacer at Process(III) was changed from 3.4 mm to 20.2 mm. Table 3 lists thecharacteristics of the obtained structure material.

Thirteenth Example

A laminate was obtained in a manner similar to the first example using afiber-reinforced mat and a resin sheet similar to those of the firstexample. Subsequently, a structure material was obtained through thefollowing processes (I) through (VI). In the obtained structurematerial, voids with the reinforced fibers as columnar supports werefound by sectional observation. Table 3 lists the characteristics of theobtained structure material.

(I) The laminate is arranged within a mold cavity for press moldingpreheated at 230° C., and the mold is closed.

(II) Subsequently, after being maintained for 120 seconds, the mold ismaintained for additional 60 seconds with a pressure of 3 MPa applied.

(III) After Process (II), the mold cavity was opened, and a spacer witha thickness of 1.2 mm was inserted into the end thereof, and the moldwas maintained for 5 seconds.

(IV) Subsequently, adjustment is performed to give a thickness of 3.4 mmwhen the structure material is obtained.

(V) Subsequently, the mold cavity is again fastened, and the cavitytemperature is decreased to 50° C. with the pressure maintained.

(VI) The mold is opened, and the structure material is taken out of it.

Fourteenth Example

A laminate was obtained in a manner similar to the first example using afiber-reinforced mat and a resin sheet similar to those of the firstexample. Subsequently, a structure material was obtained through thefollowing processes (I) through (VI). In the obtained structurematerial, voids with the reinforced fibers as columnar supports werefound by sectional observation. Table 3 lists the characteristics of theobtained structure material.

(I) The laminate is arranged within a mold cavity for press moldingpreheated at 230° C., and the mold is closed.

(II) Subsequently, after being maintained for 120 seconds, the mold ismaintained for additional 60 seconds with a pressure of 3 MPa applied.

(III) After Process (II), the mold cavity was opened, and a metallicspacer with a thickness of 2.0 mm was inserted into the end thereof, andthe mold was maintained for 20 seconds.

(IV) Subsequently, adjustment is performed to give a thickness of 3.4 mmwhen the structure material is obtained.

(V) Subsequently, the mold cavity is again fastened, and the cavitytemperature is decreased to 50° C. with the pressure maintained.

(VI) The mold is opened, and the structure material is taken out of it.

Fifteenth Example

A laminate was obtained in a manner similar to the first example using afiber-reinforced mat and a resin sheet similar to those of the firstexample. Subsequently, a structure material was obtained through thefollowing processes (I) through (VI). In the obtained structurematerial, voids with the reinforced fibers as columnar supports werefound by sectional observation. Table 3 lists the characteristics of theobtained structure material.

(I) The laminate is arranged within a mold cavity for press moldingpreheated at 230° C., and the mold is closed.

(II) Subsequently, after being maintained for 120 seconds, the mold ismaintained for additional 60 seconds with a pressure of 3 MPa applied.

(III) After Process (II), the mold cavity was opened, and metallicspacers with a thickness of 2.3 mm were inserted at regular intervalsfrom the end to the center thereof, and the mold was maintained for 20seconds.

(IV) Subsequently, the mold cavity is opened, and adjustment isperformed to give a thickness of 3.4 mm of a part not being in contactwith the metallic spacers at Process (III).

(V) Subsequently, the mold cavity is again fastened, and the cavitytemperature is decreased to 50° C. with the pressure maintained.

(VI) The mold is opened, and the structure material is taken out of it.

First Comparative Example

A laminate was prepared in which Fiber-Reinforced Mat 3 as afiber-reinforced mat and the PP resin as a resin sheet were arranged inorder of [resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet/resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet]. Subsequently, a structure material was obtained in a mannersimilar to the first example except that the metallic spacer was notused at Process (III) in the first example. Table 4 lists thecharacteristics of the obtained structure material.

Second Comparative Example

Seventy pieces of Fiber-Reinforced Mat 3 were stacked on one another,which was put between the PP resin to prepare a laminate. Subsequently,a structure material was obtained in a manner similar to the firstexample except that the thickness of the metallic spacer was changedfrom 3.4 mm to 3.2 mm at Process (III) in the first example. Table 4lists the characteristics of the obtained structure material.

Third Comparative Example

A laminate was prepared in which Fiber-Reinforced Mat 3 as afiber-reinforced mat and the PP resin as a resin sheet were arranged inorder of [resin sheet/fiber-reinforced mat/fiber-reinforced mat/resinsheet]. Subsequently, a structure material was obtained in a mannersimilar to the first example except that the thickness of the metallicspacer was changed from 3.4 mm to 1.4 mm at Process (III) in the firstexample. Table 4 lists the characteristics of the obtained structurematerial.

Fourth Comparative Example

A laminate was prepared in which Fiber-Reinforced Mat 3 as afiber-reinforced mat and the PP resin as a resin sheet were arranged inorder of [resin sheet/fiber-reinforced mat/fiber-reinforced mat/resinsheet/resin sheet/fiber-reinforced mat/fiber-reinforced mat/resinsheet/resin sheet/fiber-reinforced mat/fiber-reinforced mat/resinsheet]. Subsequently, a structure material was obtained in a mannersimilar to the first example except that the structure material wasobtained through the processes (I) through (V) in the first example.Table 4 lists the characteristics of the obtained structure material.

Fifth Comparative Example

A structure material was obtained in a manner similar to the firstexample except that Fiber-Reinforced Mat 5 was used as afiber-reinforced mat. Table 4 lists the characteristics of the obtainedstructure material.

Sixth Comparative Example

A structure material was obtained in a manner similar to the firstexample except that a molded body only through Process (I) and Process(III) in the first example was taken out of the mold and was air-cooled.Table 4 lists the characteristics of the obtained structure material.

Seventh Comparative Example

A laminate was obtained in a manner similar to the first example using afiber-reinforced mat and a resin sheet similar to those of the firstexample. Subsequently, a structure material was obtained through thefollowing processes (I) through (VI). Table 4 lists the characteristicsof the obtained structure material.

(I) The laminate is arranged within a mold cavity for press moldingpreheated at 230° C., and the mold is closed.

(II) Subsequently, after being maintained for 120 seconds, the mold ismaintained for additional 60 seconds with a pressure of 3 MPa applied.

(III) After Process (II), the mold cavity was opened, and a spacer witha thickness of 1.8 mm was inserted into the end thereof, and the moldwas maintained for 20 seconds.

(IV) Subsequently, adjustment is performed to give a thickness of 3.4 mmwhen the structure material is obtained.

(V) Subsequently, the mold cavity is again fastened, and the cavitytemperature is decreased to 50° C. with the pressure maintained.

(VI) The mold is opened, and the structure material is taken out of it.

TABLE 3 First Second Third Fourth Fifth Sixth Seventh Eighth ExampleExample Example Example Example Example Example Example StructureReinforced — Fiber- Fiber- Fiber- Fiber- Fiber- Fiber- Fiber- Fiber-material fibers Reinforced Reinforced Reinforced Reinforced ReinforcedReinforced Reinforced Reinforced Mat 3 Mat 3 Mat 3 Mat 3 Mat 3 Mat 3 Mat6 Mat 3 Polymer — PP resin PP resin PP resin PA resin PPS PC resin PPresin Epoxy resin resin Volume content of % by 6.7 9.9 3.3 6.7 6.7 6.46.7 6.4 reinforced fibers volume Volume content of % by 26.6 40.1 13.426.6 26.6 26.9 26.6 26.9 resin volume Volume content of % by 66.7 50.083.3 66.7 66.7 66.7 66.7 66.7 voids volume Specific gravity of g/cm³0.36 0.54 0.18 0.42 0.48 0.44 0.36 0.44 entire structure materialThickness of mm 3.4 3.4 5.6 3.3 2.9 3.3 3.4 3.3 structure material (St)Length of reinforced mm 6 6 6 6 6 6 6 6 fibers (Lf) Oriented angle in °4.01 2.70 13.49 3.94 3.43 3.94 4.01 3.94 sectional direction ofstructure material (θf) Lf² · (1 − cos(θf)) — 0.09 0.04 0.99 0.09 0.060.09 0.09 0.09 Resin coating around Present Present Present PresentPresent Present Present Present Present reinforced fibers or absentResin thickness μm 4.8 4.8 4.8 4.8 4.6 5.2 4.8 5.2 around reinforcedfibers Bending modulus (Ec) GPa 8.1 10.4 4.0 9.0 9.2 8.5 10.0 9.5Specific bending — 5.58 4.04 8.82 4.95 4.37 4.64 5.98 4.81 modulus NinthTenth Eleventh Twelfth Thirteenth Fourteenth Fifteenth Example ExampleExample Example Example Example Example Structure Reinforced — Fiber-Fiber- Fiber- Fiber- Fiber- Fiber- Fiber- material fibers ReinforcedReinforced Reinforced Reinforced Reinforced Reinforced Reinforced Mat 2Mat 4 Mat 1 Mat 3 Mat 3 Mat 3 Mat 3 Polymer — PP resin PP resin PP resinPP resin PP resin PP resin PP resin Volume content of % by 6.7 6.7 6.76.7 6.7 6.7 6.7 reinforced fibers volume Volume content of % by 26.626.6 26.6 26.6 26.6 26.6 26.6 resin volume Volume content of % by 66.766.7 66.7 66.7 66.7 66.7 66.7 voids volume Specific gravity of g/cm³0.36 0.36 0.36 0.36 0.36 0.50 0.50 entire structure material Thicknessof mm 3.4 3.4 3.4 20.2 3.4 3.4 3.4 structure material (St) Length ofreinforced mm 3 12 5 6 6 6 6 fibers (Lf) Oriented angle in ° 8.19 2.044.9 4.01 8.14 4.01 4.01 sectional direction of structure material (θf)Lf² · (1 − cos(θf)) — 0.37 0.02 0.13 0.09 0.36 0.09 0.09 Resin coatingaround Present Present Present Present Present Present Present Presentreinforced fibers or absent Resin thickness μm 4.8 4.8 4.8 4.8 4.8 4.84.8 around reinforced fibers Bending modulus (Ec) GPa 7.2 8.3 8.1 8.18.1 8.7 — Specific bending — 5.36 5.62 5.58 5.58 5.58 4.11 — modulus

TABLE 4 First Second Third Fourth Fifth Sixth Seventh ComparativeComparative Comparative Comparative Comparative Comparative ComparativeExample Example Example Example Example Example Example StructureReinforced — Fiber- Fiber- Fiber- Fiber- Fiber- Fiber- Fiber- materialfibers Reinforced Reinforced Reinforced Reinforced Reinforced ReinforcedReinforced Mat 3 Mat 3 Mat 3 Mat 3 Mat 5 Mat 3 Mat 3 Resin — PP resin PPresin PP resin PP resin PP resin PP resin PP resin Volume content of %by 20 60 3.3 3.3 6.7 6.7 6.7 reinforced fibers volume Volume content ofresin % by 80 6.7 13.4 13.4 26.6 26.6 26.6 volume Volume content ofvoids % by 0 33.3 83.3 83.3 66.7 66.7 66.7 volume Specific gravity ofg/cm³ 1.08 1.14 0.18 0.18 0.42 0.36 0.36 entire structure materialThickness of structure mm 2.8 3.2 1.4 3.4 3.4 3.4 3.4 material (St)Length of reinforced mm 6 6 5 5 0.5 6 6 fibers (Lf) Oriented angle in °1.34 0.65 8.04 8.04 55.6 4.01 2.04 sectional direction of structurematerial (θf) Lf² · (1 − cos(θf)) — 0.01 0.00 0.25 0.25 0.12 0.09 0.02Resin coating around Present Complete Absent Partially PartiallyPartially Absent Partially present reinforced fibers or absentimpregnation present present present Resin thickness around μm —Unmeasurable 0.5 to 30 0.5 to 30 20 Adherence 0.5 to 30 reinforcedfibers (only with uneven with uneven only to with uneven partially)density density inter- density sections of reinforced fibers Bendingmodulus (Ec) GPa 14.0 0.2 1.2 1.2 2.5 1.0 2.5 Specific bending modulus —2.23 0.51 5.90 5.90 3.23 2.78 3.23

[Consideration]

It is clear that the present example is excellent in a balance betweenthe specific bending modulus and the absolute value of the bendingmodulus owing to the fact that the thickness St of the structurematerial satisfies the conditional expression St≥Lf²·(1−cos(θf)).Furthermore, the same holds true for the fourth, the fifth, the sixth,and the eighth examples, in which the resin type was changed. Incontrast, in the first comparative example, in which thefiber-reinforced mat and the resin were similar to those of the firstexample, owing to the absence of voids, the specific bending modulus wasunable to be satisfied. In the second comparative example, in which thevolume ratios of the resin and the voids were adjusted, a balancebetween them and the volume ratio of the fiber-reinforced mat was poor,and the bending modulus was low. It is estimated that these are becausecoating by the resin around the reinforced fibers was not formed. In thethird comparative example, the bending modulus was low. This is becausethe reinforced fibers not in a nearly monofilament form were used, whichwas not improved by the fourth comparative example, in which thethickness of the structure material was changed. In the fifthcomparative example, the fiber length of the reinforced fibers wasreduced, and the conditional expression St≥Lf²·(1−cos(θf)) was unable tobe satisfied. Consequently, the absolute value of the bending moduluswas unable to be satisfied. In the sixth comparative example, thereinforced fibers were not coated with the resin, and the resin waslocalized at intersection points of the reinforced fibers, whereby theabsolute value of the bending modulus was low, although the contents ofthe reinforced fibers, the resin, and the voids were satisfied; as aresult, the value of the specific bending modulus was unable to besatisfied. In the seventh comparative example, high-specific gravityregions were provided on the surfaces, whereas a low specific gravityregion was provided at the central part; their thickness ratio was 1:1between both surfaces and the center. The bending properties of theseventh comparative example were evaluated; owing to a bad balance inthickness ratio between the regions having voids on the surfaces and theregion having voids at the center of the structure material, theproperties of the layer having a high porosity at the central part werepredominant, which made unable to obtain a desired property.

[Second Mode]

The following describes the structure material according to the secondmode of the present invention.

FIG. 1 is a schematic diagram of a sectional structure of the structurematerial according to the first and second modes of the presentinvention. As illustrated in FIG. 1, this structure material 1 accordingto the second mode of the present invention includes a resin 2,reinforced fibers 3, and voids 4.

Examples of the resin 2 include thermoplastic resins and thermosettingresins. In the present invention, a thermosetting resin and athermoplastic resin may be blended with each other; in that case, acomponent with an amount exceeding 50% by mass of the componentscontained in the resin is the name of the resin.

In one mode of the present invention, the resin 2 desirably contains atleast one thermoplastic resin. Examples of the thermoplastic resininclude thermoplastic resins selected from crystalline plastics such as“polyesters such as polyethylene terephthalate (PET), polybutyleneterephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylenenaphthalate (PEN), and liquid crystal polyesters; polyolefins such aspolyethylene (PE), polypropylene (PP), and polybutylene;polyoxymethylene (POM), polyamide (PA), and polyarylene sulfides such aspolyphenylene sulfide (PPS); polyketone (PK), polyether ketone (PEK),polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyethernitrile (PEN), and fluorine-based resins such aspolytetrafluoroethylene; and liquid crystal polymers (LCP)”, amorphousplastics such as “styrene-based resins, polycarbonate (PC), polymethylmethacrylate (PMMA), polyvinyl chloride (PVC), polyphenylene ether(PPE), polyimide (PI), polyamideimide (PAI), polyetherimide (PEI),polysulfone (PSU), polyether sulfone, and polyarylate (PAR)”,phenol-based resins, phenoxy resins, polystyrene-based,polyolefin-based, polyurethane-based, polyester-based, polyamide-based,polybutadiene-based, polyisoprene-based, and fluorine-based resins,acrylonitrile-based and other thermoplastic elastomers, and copolymersand modifieds of these. Among them, polyolefin is desirably used in viewof the lightness of an obtained structure material, polyamide isdesirably used in view of the strength thereof, amorphous plastics suchas polycarbonate and styrene-based resins are desirably used in view ofthe surface appearance thereof, polyarylene sulfides are desirably usedin view of heat resistance, polyether ether ketone is desirably used inview of the continuous use temperature thereof, and fluorine-basedresins are desirably used in view of the chemical resistance thereof.

In one mode of the present invention, the resin 2 desirably contains atleast one thermosetting resin. Examples of the thermosetting resininclude unsaturated polyesters, vinyl esters, epoxy resins, phenolresins, urea resins, melamine resins, thermosetting polyimides,copolymers and modifieds of these, and resins obtained by blending atleast two of these. The structure material according to the presentinvention may contain impact-resistant improvers such as elastomer andrubber components and other fillers and additives to the extent that theobjects of the present invention are not impaired. Examples of fillersand additives include inorganic fillers, fire retardants, conductivityimparting agents, nucleators, ultraviolet absorbers, antioxidants,damping materials, antibacterial agents, insect repellents, deodorants,anti-coloring agents, thermal stabilizers, mold release agents,antistatic agents, plasticizers, lubricants, colorants, pigments, dyes,foaming agents, anti-foaming agents, and coupling agents.

The volume content of the resin 2 is within a range of 2.5% by volume ormore and 85% by volume or less. When the volume content of the resin 2is less than 2.5% by volume, it is unable to bind the reinforced fibers3 within the structure material 1 together to make the reinforcingeffect of the reinforced fibers 3 sufficient and to satisfy themechanical characteristics especially bending properties of thestructure material, which is thus undesirable. In contrast, when thevolume content of the resin 2 is larger than 85% by volume, the resinamount is too large, and it is difficult to have a void structure, whichis thus undesirable.

Examples of the reinforced fibers 3 include metallic fibers formed ofaluminum, brass, stainless, and the like, PAN-based, rayon-based,lignin-based, and pitch-based carbon fibers, graphite fibers, insulatingfibers formed of glass and the like, organic fibers formed of aramid,PBO, polyphenylene sulfide, polyester, acrylic, nylon, polyethylene, andthe like, and inorganic fibers formed of silicon carbide, siliconnitride, and the like. Surface treatment may be applied to these fibers.Examples of the surface treatment include coating treatment with metalas a conductor, treatment with coupling agents, treatment with sizingagents, treatment with binders, and adhesion treatment for additives.One of these fibers may be used alone, or two or more of them may beused in combination. Among them, PAN-based, pitch-based, and rayon-basedcarbon fibers, which are excellent in specific strength and specificstiffness, are desirably used in view of a weight reduction effect.Glass fibers are desirably used in view of increasing the economy of theobtained structure material; carbon fibers and glass fibers aredesirably used in combination in view of a balance between mechanicalcharacteristics and economy in particular. Furthermore, aramid fibersare desirably used in view of increasing the impact absorption andshaping property of the obtained structure material; carbon fibers andaramid fibers are desirably used in combination in view of a balancebetween mechanical characteristics and impact absorption in particular.Reinforced fibers coated with metal such as nickel, copper, or ytterbiumcan also be used in view of increasing the conductivity of the obtainedstructure material. Among them, PAN-based carbon fibers, which areexcellent in strength and mechanical characteristics such as modulus,are more desirably used.

The reinforced fibers 3 are desirably discontinuous and dispersed in anearly monofilament form and in a random manner. The reinforced fibers 3are prepared in such a manner, whereby when a sheet-shaped structureprecursor or structure material is molded by applying external force,shaping into a complex shape is made easy. In addition, the reinforcedfibers 3 are prepared in such a manner, whereby voids formed by thereinforced fibers 3 become fine, and weak parts at fiber bundle ends ofthe reinforced fibers 3 in the structure material 1 can be minimized,and thus giving isotropy in addition to excellent reinforcing efficiencyand reliability. The nearly monofilament indicates that a reinforcedfiber single yarn is present as less than 500 fine-denier strands. Thereinforced fibers 3 are more desirably dispersed in a monofilament form.

Being dispersed in a nearly monofilament form or monofilament formindicates that, for a reinforced fiber 3 freely selected in thestructure material 1, the rate of single filaments having atwo-dimensional contact angle of 1° or more (hereinafter, also referredto as a fibers dispersed rate) is 80% or more or, in other words, that abundle in which two or more single filaments in the structure material 1are in contact with each other to be parallel to each other is less than20%. Consequently, the mass fraction of a fiber bundle with a filamentnumber of 100 or less at least in the reinforced fibers 3 particularlypreferably corresponds to 100%.

The two-dimensional contact angle refers to an angle formed by a singlefilament and a single filament being in contact with this singlefilament in the case of discontinuous reinforced fibers and is definedas an angle on an acute angle side within a range of 0° or more and 90°or less out of angles formed by the single filaments being in contactwith each other. The following further describes this two-dimensionalcontact angle with reference to a drawing. FIG. 2 is a schematic diagramof an example of a dispersion state of the reinforced fibers in afiber-reinforced mat when observed in a planar direction (FIG. 2(a)) anda thickness direction (FIG. 2(b)). With reference to a single filament11 a, the single filament 11 a is observed to cross single filaments 11b to 11 f in FIG. 2(a), whereas the single filament 11 a is not incontact with the single filaments 11 e and 11 f in FIG. 2(b). In thiscase, the single filaments 11 b to 11 d are objects for which thetwo-dimensional contact angle is evaluated for the single filament 11 aas the reference; the two-dimensional contact angle is an angle A on theacute angle side within a range of 0° or more and 90° or less out of thetwo angles formed by the two single filaments being in contact with eachother.

A method for measuring the two-dimensional contact angle is not limitedto a particular method; a method can be exemplified that observes theorientation of the reinforced fibers 3 from a surface of the structurematerial 1, for example. In this case, the surface of the structurematerial 1 is polished to expose the reinforced fibers 3, whereby thereinforced fibers 3 become easier to be observed. Another example thatcan be exemplified is a method that performs X-ray CT transmissionobservation to take an orientation image of the reinforced fibers 3. Forthe reinforced fibers 3 having high X-ray transmissivity, fibers for atracer are mixed into the reinforced fibers 3, or a chemical for atracer is applied to the reinforced fibers 3, whereby the reinforcedfibers 3 become easier to be observed, which is thus desirable. Whenmeasurement is difficult by the methods, a method can be exemplifiedthat puts the structure material 1 into a high-temperature environmentsuch as an oven to burn off a resin component and then observes theorientation of the reinforced fibers 3 from the reinforced fibers 3 thathave been taken out using an optical microscope or an electronmicroscope.

The fibers dispersed rate is measured by the following procedure basedon the method of observation described above. Specifically, thetwo-dimensional contact angle is measured for all the single filaments(the single filaments 11 b to 11 d in FIG. 2) being in contact with asingle filament selected at random (the signal filament 11 a in FIG. 2).This measurement is performed for 100 single filaments, and a rate iscalculated from the ratio of the number of signal filaments having atwo-dimensional contact angle of 1° or more to the total number of allthe single filaments for which the two-dimensional contact angle ismeasured.

Furthermore, the reinforced fibers 3 are particularly desirablydispersed in a random manner. The reinforced fibers 3 being dispersed ina random manner refers to the fact that the arithmetic mean of atwo-dimensional oriented angle of a reinforced fiber 3 freely selectedin the structure material 1 is within a range of 30° or more and 60° orless. The two-dimensional oriented angle refers to an angle formed by asingle filament of the reinforced fiber 3 and a single filament crossingthis single filament and is defined as an angle on an acute angle sidewithin a range of 0° or more and 90° or less out of angles formed by thesingle filaments crossing each other.

The following further describes this two-dimensional oriented angle withreference to a drawing. In FIGS. 2(a) and (b), with reference to thesingle filament 11 a, the single filament 11 a crosses the other singlefilaments 11 b to 11 f. The crossing means a state in which a singlefilament as a reference is observed to cross other single filaments on atwo-dimensional plane observed, does not necessarily require the singlefilament 11 a and the single filaments 11 b to 11 f to be in contactwith each other, and does not exclude a state in which the singlefilament 11 a is observed to cross the single filaments 11 b to 11 fwhen viewed in a projected manner. In other words, focusing on thesingle filament 11 a as the reference, all the single filaments 11 b to11 f are objects for which the two-dimensional oriented angle isevaluated; in FIG. 2(a), the two-dimensional oriented angle is the angleA on the acute angle side within a range of 0° or more and 90° or lessout of the two angles formed by the two crossing single filaments.

A method for measuring the two-dimensional oriented angle is not limitedto a particular method; a method can be exemplified that observes theorientation of the reinforced fibers 3 from a surface of the structureelement, for example, for which means similar to the method formeasuring the two-dimensional contact angle described above can beemployed. The mean of the two-dimensional oriented angle is measured bythe following procedure. Specifically, the mean of the two-dimensionaloriented angle is measured for all the single filaments (the singlefilaments 11 b to 11 f in FIG. 2) crossing a single filament selected atrandom (the signal filament 11 a in FIG. 2). When there are a largenumber of other single filaments crossing a single filament, forexample, an arithmetic mean measured by selecting 20 other crossingsingle filaments at random may be substituted. This measurement isrepeated a total of five times with reference to other single filaments,and its arithmetic mean is calculated as the arithmetic mean of thetwo-dimensional oriented angle.

The reinforced fibers 3 are dispersed in a nearly monofilament form andin a random manner, whereby the performance given by the reinforcedfibers 3 dispersed in a nearly monofilament form described above can beincreased to the maximum. In addition, isotropy can be imparted to themechanical characteristics of the structure material 1. In view of theforegoing, the fibers dispersed rate of the reinforced fibers 3 isdesirably 90% or more and more desirably closer to 100%. The arithmeticmean of the two-dimensional oriented angle of the reinforced fibers 3 isdesirably within a range of 40° or more and 50° or less and moredesirably closer to 45°, which is an ideal angle.

Examples of the reinforced fibers 3 not having a nonwoven fabric-likeform include a sheet substrate, a woven fabric substrate, and anon-crimped substrate in which the reinforced fibers 3 are arranged inone direction. These forms arrange the reinforced fibers 3 regularly anddensely, and thus there are few voids 4 in the structure material 1,which makes the impregnation of the resin 2 extremely difficult and mayform a non-impregnated part or significantly restrict alternatives aboutimpregnating means and/or resin type.

The form of the reinforced fibers 3 may be any of a continuousreinforced fiber having a length similar to that of the structurematerial 1 and a discontinuous reinforced fiber with a finite length cutinto a certain length; it is desirably a discontinuous reinforced fiberin view of easily impregnating the reinforced fibers 3 with the resin 2or being able to easily adjust the amount of the resin 2.

The volume content of the reinforced fibers 3 is within a range of 0.5%by volume or more and 55% by volume or less. When the volume content ofthe reinforced fibers 3 is less than 0.5% by volume, the reinforcingeffect caused by the reinforced fibers 3 is unable to be sufficient,which is thus undesirable. In contrast, when the volume content of thereinforced fibers 3 is larger than 55% by volume, the volume content ofthe resin 2 relative to the reinforced fibers 3 is relatively low, andit is unable to bind the reinforced fibers 3 within the structurematerial 1 together to make the reinforcing effect of the reinforcedfibers 3 sufficient and to satisfy the mechanical characteristicsespecially bending properties of the structure material 1, which is thusundesirable.

The reinforced fibers 3 are coated with the resin 2, in which thethickness of the resin 2 is preferably within a range of 1 μm or moreand 15 μm or less. As to the coated state of the reinforced fibers 3coated with the resin 2, coating at least intersection points of thesingle filaments of the reinforced fibers 3 contained in the structurematerial 1 is sufficient in view of the shape stability of the structurematerial 1 and the easiness and the degree of freedom in thicknesscontrol; as a more desirable manner, the resin 2 is desirably coatedaround the reinforced fibers 3 with the above thickness. This statemeans that the surface of the reinforced fibers 3 is not exposed owingto the resin 2 or, in other words, that the reinforced fibers 3 form anelectric wire-shaped coating by the resin 2. This formation furthercauses the structure material 1 to have shape stability and makes itsexpression of mechanical characteristics sufficient. In addition, thecoated state of the reinforced fibers 3 coated with the resin 2 is notrequired to be coated across the whole of the reinforced fibers 3 andmay be within a range in which the shape stability, the bending modulus,and the bending strength of the structure material 1 according to thepresent invention are not impaired.

The longer of the mass mean fiber length of the reinforced fibers 3 isdesirably within a range of 1 mm or more and 15 mm or less. With thislength, the reinforcing efficiency of the reinforced fibers 3 can beincreased, and thus excellent mechanical characteristics can be impartedto the structure material 1. When the longer of the mass mean fiberlength of the reinforced fibers 3 is less than 1 mm, the voids 4 withinthe structure material 1 are unable to be formed efficiently, and thespecific gravity may increase; in other words, it is difficult to obtainthe structure material 1 with a desired thickness even with the samemass, which is thus undesirable. In contrast, when the longer of themass mean fiber length of the reinforced fibers 3 is longer than 15 mm,the reinforced fibers 3 are likely to bend by their self-weight withinthe structure material 1 to cause the expression of mechanicalcharacteristics to be hindered, which is thus undesirable. The resincomponent of the structure material 1 is removed by a method such asburning or eluting, 400 remaining reinforced fibers 3 are selected atrandom, and the lengths thereof are measured down to 10 μm; the longerof the mass mean fiber length can be calculated as the mean lengththereof.

The voids 4 in the present invention each indicate a space formed by thereinforced fibers 3 coated with the resin 2 serving as columnar supportsand overlapping with each other or crossing each other. When a structureprecursor in which the reinforced fibers 3 are impregnated with theresin 2 in advance is heated to obtain a structure material, forexample, the melting or softening of the resin 2 along with heatingraises the reinforced fibers 3 to form the voids 4. This phenomenon isbased on the property of the reinforced fibers 3 inside the structureprecursor in a compressed state by pressurization rising by hair raisingforce caused by their modulus. The content of the voids 4 in thestructure material 1 is within a range of 10% by volume or more and 99%by volume or less. When the content of the voids 4 is less than 10% byvolume, the specific gravity of the structure material 1 is high, andlightness is not satisfied, which is thus undesirable. In contrast, whenthe content of the voids 4 is larger than 99% by volume or, in otherwords, the thickness of the resin 2 coated around the reinforced fibers3 is small, and the reinforcing of the reinforced fibers 3 in thestructure material 1 is not performed sufficiently to decreasemechanical characteristics, which is thus undesirable. The upper limitof the content of the voids 4 is desirably 97% by volume. In the presentinvention, as to the volume content, the sum of the respective volumecontents of the resin 2, the reinforced fibers 3, and the voids 4included in the structure material 1 is defined as 100% by volume.

A thickness St of the structure material 1 satisfies a conditionalexpression St≥Lf²·(1−cos(θf)) where the length of the reinforced fibers3 is Lf and the oriented angle of the reinforced fibers 3 in a sectionaldirection of the structure material 1 is θf. The thickness St of thestructure material 1 not satisfying the conditional expression indicatesthat the reinforced fibers 3 in the structure material 1 are bending orthat a balance between the structure material 1 with a desired thicknessand a fiber length is poor. This indicates that the structure material 1is poor in the degree of freedom in thickness design because the featureof the charged reinforced fibers 3 is unable to be sufficientlyexpressed, and furthermore, as to characteristics using the tensilestrength and the tensile modulus of the reinforced fibers 3 among themechanical characteristics of the structure material 1, an efficientreinforcing effect is unable to be obtained because the straightness ofthe reinforced fibers 3 is lost, which is thus undesirable. In theconditional expression, the value is preferably within a range of 2% ormore and 20% or less of the thickness St of the structure material 1 andparticularly preferably within a range of 5% or more and 18% or lessthereof considering that a balance can be obtained between bendingmodulus and specific bending modulus as the characteristics of thestructure material 1 formed by the length and the oriented angle of thereinforced fibers 3 and that owing to the fiber length and its orientedangle in the structure material 1, deformation in a state beforesolidification or curing during a molding process is easily performed tofacilitate the molding of the desired structure material 1. The unitsused for the conditional expression are St [mm], Lf [mm], and θf [°].

The length Lf of the reinforced fibers 3 can be calculated as the longerof the mass mean fiber length calculated from the lengths obtained byremoving the resin component of the structure material 1 by a methodsuch as burning or eluting, selecting 400 remaining reinforced fibers 3at random, and measuring the lengths thereof down to 10 μm. The orientedangle θf of the reinforced fibers 3 in the sectional direction of thestructure material 1 is the degree of inclination relative to thesectional direction of the structure material 1 or, in other words, thedegree of inclination of the reinforced fibers 3 relative to thethickness direction. A larger value indicates that the reinforced fibers3 are inclined in an upright manner in the thickness direction, and thevalue is given within a range of 0° or more and 90° or less. In otherwords, the oriented angle θf of the reinforced fibers 3 is set to bewithin the range, whereby reinforcing function in the structure material1 can be expressed more effectively. The upper limit of the orientedangle θf of the reinforced fibers 3, which is not limited to aparticular value, is desirably 60° or less and more desirably 45° orless in view of the expression of bending modulus as the structurematerial 1. When the oriented angle θf of the reinforced fibers 3 isless than 3°, the reinforced fibers 3 in the structure material 1 areoriented in a planar manner or, in other words, a two-dimensionalmanner, and the degree of freedom in the thickness of the structurematerial 1 decreases, and lightness is unable to be satisfied, which isthus undesirable. For this reason, the oriented angle θf of thereinforced fibers 3 is preferably 3° or more.

The oriented angle θf of the reinforced fibers 3 can be measured basedon observation of a perpendicular section relative to the planardirection of the structure material 1. FIG. 3 is a schematic diagram ofan example of sectional structures in the planar direction (FIG. 3(a))and the thickness direction (FIG. 3(b)) of the structure materialaccording to the first and second modes of the present invention. InFIG. 3(a), the sections of reinforced fibers 3 a and 3 b areapproximated to an oval shape in order to simplify measurement. In thesection of the reinforced fiber 3 a, its aspect ratio of the oval (=ovalmajor axis/oval minor axis) is viewed to be smaller, whereas in thesection of the reinforced fiber 3 b, its aspect ratio of the oval isviewed to be larger. Meanwhile, according to FIG. 3(b), the reinforcedfiber 3 a has an inclination nearly parallel relative to a thicknessdirection Y, whereas the reinforced fiber 3 b has a certain amount ofinclination relative to the thickness direction Y. In this case, as tothe reinforced fiber 3 b, an angle θx formed by a planar direction X ofthe structure material 1 and a fiber principal axis (the major axialdirection in the oval) α is nearly equal to an out-of-plane angle θf ofthe reinforced fiber 3 b. In contrast, as to the reinforced fiber 3 a,there is a large deviation between the angle θx and the oriented angleθf, and it cannot be said that the angle θx is reflective of theoriented angle θf. Consequently, when the oriented angle θf is read fromthe perpendicular section relative to the planar direction of thestructure material 1, the aspect ratio of the oval of a fiber sectionhaving a certain value or more is extracted, whereby the accuracy ofdetecting the oriented angle θf can be increased.

For an indicator of the aspect ratio of the oval to be extracted, amethod can be employed that when the sectional shape of the singlefilament is close to a perfect circle or, that is, when a fiber aspectratio in a section perpendicular to the longitudinal direction of thereinforced fibers is 1.1 or less, the angle θx formed by the planardirection X and the fiber principal axis α is measured for thereinforced fibers 3 having an aspect ratio of the oval of 20 or more,and this angle is employed as the oriented angle θf. In contrast, whenthe sectional shape of the single filament is an oval shape, a cocoonshape or the like, in which the fiber aspect ratio is larger than 1.1,it is better to focus on the reinforced fibers 3 having a larger aspectratio of the oval to measure the oriented angle θf; the reinforcedfibers 3 having an aspect ratio of the oval of 30 or more when the fiberaspect ratio is 1.1 or more and less than 1.8, having an aspect ratio ofthe oval of 40 or more when the fiber aspect ratio is 1.8 or more andless than 2.5, and having an aspect ratio of the oval of 50 or more whenthe fiber aspect ratio is 2.5 or more may be selected, and the orientedangle θf thereof may be measured.

The specific bending modulus of a first part of the structure material 1represented as Ec^(1/3)·ρ⁻¹ is within a range of 1 or more and less than3 where the bending modulus of the structure material 1 is Ec and thespecific gravity of the structure material 1 is ρ. When the specificbending modulus of the first part of the structure material 1 is lessthan 1, the weight reduction effect of the structure material 1 is lost,which is thus undesirable. In contrast, when the specific bendingmodulus of the first part of the structure material 1 is larger than 3,that means that the bending modulus is low when the structure material 1is formed of a single composition, which is thus undesirable. Moredesirably, the specific bending modulus of the first part of thestructure material 1 is less than 3 exceeding 2.3, which is a generalspecific bending modulus of carbon fiber-reinforced plastic compositematerials attracting attention for their weight reduction effect.

The specific bending modulus of a second part of the structure material1 different from the first part is within a range of 3 or more and 20 orless. When the specific bending modulus of the second part of thestructure material 1 is less than 3, even if the bending modulus ishigh, the specific gravity is also high, and a desired weight reductioneffect is unable to be obtained, which is thus undesirable. In contrast,when the specific bending modulus of the second part of the structurematerial 1 is larger than 20, it is indicated that the bending modulusis low, although the weight reduction effect is sufficient; it isdifficult to maintain a shape desired as the structure material 1, andthe bending modulus of the structure material 1 itself is poor, which isthus undesirable. The specific bending modulus of steel materials andaluminum is 1.5 or less in general; the region of the specific bendingmodulus extremely excellent compared with these metallic materials isachieved. Furthermore, the specific bending modulus of the second partof the structure material 1 is 3 or more exceeding 2.3, which is ageneral specific bending modulus of carbon fiber-reinforced plasticcomposite materials attracting attention for their weight reductioneffect, and further desirably 5 or more.

The bending modulus Ec of the second part of the structure material 1 isdesirably 6 GPa or more. The upper limit of the bending modulus is notlimited; it is generally preferably 6 GPa or more because the bendingmodulus presents no problem when the structure material 1 is designed asa member. Furthermore, the bending modulus desirably has isotropy inview of the degree of freedom in design in actual members. In contrast,the upper limit is not set for the bending modulus so long as theeffects of the present invention are not impaired; in the structurematerial according to the present invention, about 30 GPa can be theupper limit in view of relation between the volume content and thebending modulus of the reinforced fibers, the resin, and the voids. Thebending modulus being 30 GPa or more indicates in general that thecontent of the reinforced fibers is high and that the volume content ofthe voids is low, which may lead to a high specific gravity and anincrease in the weight of a product.

As illustrated in FIG. 4, first parts R1 and a second part R2 of thestructure material 1 may be present at different positions in thethickness direction of the structure material 1. As illustrated in FIG.5, the first parts R1 and the second part R2 of the structure material 1may be present at different positions in the planar direction of thestructure material. As illustrated in FIG. 4, when the specific gravityof the first parts R1 is high or, in other words, when there are fewvoids, the first parts R1 function as skin layers represented by what iscalled a sandwich structure or the like. Specifically, the skin layersas skins can contribute to an increase in the bending modulus.Furthermore, when the specific gravity of the second part R2 is low or,in other words, when there are many voids, the second part R2 functionsas a core layer represented by what is called a sandwich structure orthe like. Specifically, the core layer as a core material does notcontribute to an increase in the bending modulus very much, and only itsspecific gravity is effectively used; in addition, the thickness has alarge effect on the bending stiffness of the structure material 1, andthus a light, highly stiff structure material can be achieved. In FIG.5, parts bearing various kinds of loads are high in specific gravity,that is, the first parts R1, whereas a part bearing almost no load isthe second part R2, whereby design efficient for the lightness of thestructure material can be performed. Furthermore, the thickness of thesecond part R2 is made larger than that of each of the first parts R1,whereby the bending stiffness of the entire structure material can bedesigned, and deformation such as warpage or twist in a molded objectwhen being made into a product can be reduced. Furthermore, in thestructure material according to the present invention, the shapesillustrated in FIG. 5 and FIG. 6 can be obtained from a singlecomposition and structure precursor, and deformation and a faulty jointcaused by a coefficient of linear expansion causing a problem in thecomposition of heterogeneous materials are not required to be regardedas a problem, which is desirable.

Furthermore, the porosity of the first part of the structure material 1is desirably within a range of 0% by volume or more and less than 10% byvolume, and the porosity of the residual part is desirably within arange of 10% by volume or more and 99% by volume or less. With thisporosity, even with a single composition, the first part and the secondpart are formed as described above, whereby the part contributing thestiffness can be used as the first part, and design efficient for thelightness of the structure material can be performed. Furthermore, thethickness of the second part of is made larger than that of the firstpart, whereby the bending stiffness of the entire structure material canbe designed, weight reduction can be partially performed.

The oriented angle θf of the reinforced fibers 3 of the first part ofthe structure material 1 is desirably within a range of 5° or more and15° or less, and the oriented angle θf of the reinforced fibers 3 atother positions is desirably within a range of 5° or more and 45° orless. Not limited to a case in which the structure material is obtainedfrom a single composition, the oriented angle θf of the first part beingwithin a range of 5° or more and 15° or less means that the reinforcedfibers 3 are oriented in the planar direction; consequently, thereinforced fibers 3 bear loads, and thus in-plane strength can beincreased. Furthermore, the oriented angle θf of the second part beingwithin a range of 5° or more and 45° or less enables voids to be formedefficiently in the structure material; consequently, weight reductioncan be achieved. The oriented angle of the first part is desirablywithin a range of 5° or more and 10° or less, and the oriented angle ofthe second part is desirably within a range of 5° or more and 30° orless in view of a balance between compression characteristics andlightness as the structure material.

The specific gravity ρ of the structure material 1 is desirably 0.9g/cm³ or less. When the specific gravity ρ of the structure material 1is larger than 0.9 g/cm³, that means that mass as the structure material1 increases, resulting in an increase in mass when being made into aproduct, which is thus undesirable. The lower limit of the specificgravity is not limited; in a structure material formed of reinforcedfibers and a resin in general, a value calculated from the respectivevolume ratios of the reinforced fibers, the resin, and the voids as itscomponents can be the lower limit. In the structure material accordingto the present invention, both when the structure material is used aloneand when it is used in combination with another member, the specificgravity of the structure material itself is desirably 0.03 g/cm³ or morein view of maintaining the mechanical characteristics of the structurematerial, although it varies depending on the reinforced fibers and theresin used.

The reinforced fibers 3 in the present invention desirably have anonwoven fabric-like form in view of the easiness of the impregnation ofthe resin 2 into the reinforced fibers 3. Furthermore, the reinforcedfibers 3 have a nonwoven fabric-like form, whereby in addition to easyhandleability of the nonwoven fabric itself, impregnation can be madeeasy even in the case of thermoplastic resins, which are generally highin viscosity, which is thus desirable. The nonwoven fabric-like shapeindicates a form in which strands and/or monofilaments of the reinforcedfibers 3 are dispersed irregularly in a planar form; examples thereofinclude a chopped strand mat, a continuous strand mat, a paper-makingmat, a carding mat, and an air-laid mat (hereinafter, referred tocollectively as a fiber-reinforced mat).

Examples of a method for manufacturing the fiber-reinforced mat includedin the structure material 1 include a method for manufacturing thefiber-reinforced mat by dispersing the reinforced fibers 3 in a strandand/or a nearly monofilament form in advance. Examples of the method formanufacturing the fiber-reinforced mat include a dry process such as anair-laid method that disperses the reinforced fibers 3 to form a sheetwith an airflow and a carding method that shapes the reinforced fibers 3while mechanically carding them to form a sheet and a wet process byRadright method that stirs the reinforced fibers 3 in the water to makepaper as known techniques. Examples of means for making the reinforcedfibers 3 closer to a monofilament form include in the dry process amethod that provides fiber-opening bars, a method that vibratesfiber-opening bars, a method that makes meshes of a card finer, and amethod that adjusts the rotational speed of a card. Examples thereofinclude in the wet process a method that adjusts the stirring conditionof the reinforced fibers 3, a method that dilutes a reinforced fiberconcentration of a dispersion, a method that adjusts the viscosity of adispersion, and a method that inhibits an eddy when a dispersion istransferred. In particular, the fiber-reinforced mat is desirablymanufactured by the wet process, and the concentration of charged fibersis increased or the flow rate (flow) of a dispersion and the speed of amesh conveyor are adjusted, whereby the rate of the reinforced fibers 3in the fiber-reinforced mat can be easily adjusted. The speed of themesh conveyor is decreased relative to the flow rate of the dispersion,whereby the orientation of fibers in an obtained fiber-reinforced mat isdifficult to be directed to a taking direction, and a bulkyfiber-reinforced mat can be manufactured, for example. Thefiber-reinforced mat may be formed of the reinforced fibers 3 alone. Thereinforced fibers 3 may be mixed with a matrix resin component in apowdery form or a fibrous form. The reinforced fibers 3 may be mixedwith organic compounds or inorganic compounds. The reinforced fibers 3may be bonded to each other with a resin component.

Furthermore, the fiber-reinforced mat may be impregnated with the resin2 in advance to form a structure precursor. For a method formanufacturing the structure precursor according to the presentinvention, a method that applies pressure to the fiber-reinforced matwith the resin 2 being in a state heated at a temperature melting orsoftening or more to impregnate the fiber-reinforced mat therewith isdesirably used in view of the easiness of manufacture. Specifically, amethod that melt-impregnates the fiber-reinforced mat with a laminatearranging the resin 2 from both sides in the thickness direction can bedesirably exemplified.

For equipment for implementing the methods, a compression moldingmachine or a double belt press can be suitably used. The former is for abatch type; an intermittent type press system arranging two or moremachines for heating and cooling in a row can improve productivity. Thelatter is for a continuous type, which can easily perform continuousprocessing and is thus excellent in continuous productivity.

In manufacturing the structure material 1 according to the presentinvention, a method that manufactures it by at least the followingprocesses [1] and [2] is preferably employed in view of the easiness ofmanufacture.

Process [1]: a process for applying pressure with the resin 2 heated ata temperature melting or softening or more and impregnating thefiber-reinforced mat with the resin 2 to prepare a structure precursor

Process [2]: a process for performing thickness adjustment with thestructure precursor heated to swell it

Process [2] is a process for performing thickness adjustment with thestructure precursor obtained at Process [1] heated to swell it. Thetemperature heated in this process preferably gives an amount of heatsufficient for melting or softening the resin 2 when the resin 2included in the structure material 1 is a thermoplastic resin in view ofthe thickness control and the manufacturing speed of the structurematerial 1 to be manufactured; specifically, a temperature that ishigher than a melting temperature by 10° C. or more and is the thermaldecomposition temperature of the thermoplastic resin or less ispreferably given. When a thermosetting resin is used as the resin 2, anamount of heat sufficient for melting or softening a thermosetting resinraw material before it forms a crosslinked to be cured is preferablygiven in view of the thickness control and the manufacturing speed ofthe structure material 1 to be manufactured.

A method for performing thickness control is not limited to a particularmethod so long as it can control the heated structure precursor to be atarget thickness; a method that restricts the thickness using metallicplates or the like and a method that performs thickness control bypressure given to the structure precursor are exemplified in view of theeasiness of manufacture. For equipment for implementing the methods, acompression molding machine or a double belt press can be suitably used.The former is for a batch type; an intermittent type press systemarranging two or more machines for heating and cooling in a row canimprove productivity. The latter is for a continuous type, which caneasily perform continuous processing and is thus excellent in continuousproductivity.

Examples of the fiber-reinforced mat not having a nonwoven fabric-likeform include a sheet substrate, a woven fabric substrate, and anon-crimped substrate in which the reinforced fibers 3 are arranged inone direction. These forms arrange the reinforced fibers 3 regularly anddensely, and thus there are few voids in the fiber-reinforced mat, andthe thermoplastic resin does not form a sufficient anchoring structure,and thus when it is made into a core forming layer, bonding abilitydecreases. In addition, when the resin 2 is a thermoplastic resin,impregnation is extremely difficult, which forms a non-impregnated partor significantly restricts alternatives about impregnating means orresin type.

In the present invention, to the extent that the features of the presentinvention are not impaired, a sandwich structure using the structurematerial 1 or the structure precursor as a core layer and using anintermediate sheet material in which the reinforced fibers 3 in acontinuous form are impregnated with a resin as a skin layer is alsofeasible. The reinforced fibers 3 in a continuous form are continuouswith a length of 100 mm or more at least in one direction; many arearranged in one direction to form an aggregate, or what is called areinforced fiber bundle, which is continuous across the entire length ofthe sandwich structure. Examples of the form of the intermediate sheetmaterial formed of the reinforced fibers 3 in a continuous form includea woven fabric including reinforced fiber bundles formed of manyreinforced fibers 3 in a continuous form, a reinforced fiber bundle inwhich many reinforced fibers 3 in a continuous form are arranged in onedirection (a unidirectional fiber bundle), and a unidirectional wovenfabric including this unidirectional fiber bundle. The reinforced fibers3 may include a plurality of fiber bundles of the same form or include aplurality of fiber bundles of different forms. The number of thereinforced fibers included in one reinforced fiber bundle is normally300 to 48,000; in view of the manufacture of prepregs and themanufacture of woven fabrics, the number is desirably 300 to 24,000 andmore desirably 1,000 to 12,000.

To control the bending modulus, lamination with the direction of thereinforced fibers 3 changed is desirably used. In particular, inefficiently increasing the modulus and strength of the sandwichstructure, a continuous reinforced fiber with fiber bundles aligned inone direction (referred to as UD) is desirably used.

Examples of the structure material 1 include electric and electronicdevice parts such as “housings, trays, chassis, interior members, andcases of personal computers, displays, OA devices, cellular phones,mobile information terminals, PDAs (mobile information terminals such aselectronic notepads), video cameras, optical devices, audio devices, airconditioners, lighting devices, entertainment goods, toy goods, andother home appliances”; “various kinds of members, various kinds offrames, various kinds of hinges, various kinds of arms, various kinds ofwheel axles, various kinds of bearings for wheels, and various kinds ofbeams”; “outer plates and body parts such as hoods, roofs, doors,fenders, trunk lids, side panels, rear end panels, front bodies, underbodies, various kinds of pillars, various kinds of members, variouskinds of frames, various kinds of beams, various kinds of supports,various kinds of rails, and various kinds of hinges”; “exterior partssuch as bumpers, bumper beams, moldings, under covers, engine covers,current plates, spoilers, cowl louvers, and aerodynamic parts”;“interior parts such as instrument panels, seat frames, door trims,pillar trims, steering wheels, and various kinds of modules”; structureparts for automobiles and two-wheeled vehicles such as “motor parts, CNGtanks, and gasoline tanks”; parts for automobiles and two-wheeledvehicles such as “battery trays, headlamp supports, pedal housings,protectors, lamp reflectors, lamp housings, noise shields, and sparetire covers”; building materials such as “wall members such as soundinsulation walls and soundproofing walls”; and parts for aircraft suchas “landing gear pods, winglets, spoilers, edges, rudders, elevators,fairings, ribs, and seats”. In view of mechanical characteristics, thestructure material 1 is desirably used for automobile interior andexterior, electric and electronic device housings, bicycles, structurematerials for sporting goods, aircraft interior materials, boxes fortransportation, and building materials. Among them, the structurematerial 1 is suitable for module members including a plurality of partsin particular.

Examples

The following describes the present invention in more detail withreference to examples.

(1) Volume Content Vf of Reinforced Fibers in Structure Material

After a mass Ws of a structure material was measured, the structurematerial was heated at 500° C. for 30 minutes in the air to burn off aresin component, a mass Wf of remaining reinforced fibers was measured,and a volume content Vf was calculated by the following expression.

Vf (% by volume)=(Wf/ρf)/{Wf/ρf+(Ws−Wf)/pr}×100

ρf: the density of the reinforced fibers (g/cm³)ρr: the density of the resin (g/cm³)

(2) Bending Test on Structure Material

Test pieces were cut out of the structure material, and the bendingmodulus of the entire structure material was measured in accordance withISO 178 Method (1993). Furthermore, the first part and the second partwere separated from each other using a cutter; bending modulus wasmeasured in a similar manner for each of them. As to these test pieces,test pieces cut out in four directions including a 0° direction freelyset and +45°, −45°, and 90° directions were prepared. The number ofmeasurement n=5 was set for each of the directions, and its arithmeticmean was defined as a bending modulus Ec. As to a measurement apparatus,“INSTRON” (registered trademark) model 5565 universal material testingsystem (manufactured by INSTRON JAPAN Co., Ltd.) was used. From theobtained result, the specific bending modulus of the structure materialwas calculated by the following expression.

Specific bending modulus=Ec ^(1/3)/ρ

(3) Oriented Angle θf of Reinforced Fibers of Structure Material

A piece with a width of 25 mm was cut out of the structure material, wasembedded in an epoxy resin and was polished so as to cause aperpendicular section in a sheet thickness direction to be a surface tobe observed to prepare a sample. The sample was magnified 400 times witha laser microscope (VK-9510 manufactured by KEYENCE CORPORATION) toobserve a fiber sectional shape. An observed image was developed ontomulti-purpose image analysis software, an individual fiber sectionviewed in the observation image was extracted using a computer programincorporated in the software, an oval inscribed in the fiber section wasprovided, and the shape of the fiber section was approximated thereto(hereinafter, referred to as a fiber oval). Furthermore, for a fiberoval with an aspect ratio, which is represented by a major axial lengthα/a minor axial length β of the fiber oval, of 20 or more, an angleformed by the planar direction X and a major axial direction of thefiber oval was determined. The operation was repeated for samples to beobserved extracted from different parts of the structure material,whereby oriented angles were measured for a total of 600 reinforcedfibers, and their arithmetic mean was determined to be the orientedangle θf of the reinforced fibers.

(4) Specific Gravity ρ of Structure Material

A test piece was cut out of the structure material, and an apparentspecific gravity of the structure material was measured with referenceto JIS K7222 (2005). The dimensions of the test piece were 100 mm longand 100 mm wide. The length, width, and thickness of the test piece weremeasured with a micrometer, and a volume V of the test pieces wascalculated from the obtained values. A mass M of the cut-out test piecewas measured with an electronic balance. The obtained mass M and volumeV were substituted into the following expression to calculate a specificgravity ρ of the structure material.

ρ[g/cm³]=10³ ×M[g]/V [mm³]

(5) Volume Content of Voids of Structure Material

A test piece of 10 mm long and 10 mm wide was cut out of the structurematerial, and a section was observed with a scanning electron microscope(SEM) (model S-4800 manufactured by Hitachi High-TechnologiesCorporation) to photograph ten sites at regular intervals from thesurface of the structure material with a 1,000-fold magnification. Foreach image, an area A_(a) of voids within the image was determined.Furthermore, the area A_(a) of the voids was divided by the area of theentire image to calculate a porosity. The volume content of the voids ofthe structure material was determined by an arithmetic mean from theporosity at a total of 50 sites photographed at ten sites each for fivetest pieces.

(6) Thickness of Resin with which Reinforced Fibers are Coated

A test piece of 10 mm long and 10 mm wide was cut out of the structurematerial, and a section was observed with a scanning electron microscope(SEM) (model S-4800 manufactured by Hitachi High-TechnologiesCorporation) to photograph ten sites freely selected with a 3,000-foldmagnification. From 50 sites freely selected in which sections of thereinforced fibers were cut in an obtained image, a coating thickness ofthe resin with which the reinforced fibers were coated was measured. Forthe thickness of the resin with which the reinforced fibers were coated,the arithmetic mean of the measurement results at the 50 sites was used.

[Carbon Fiber 1]

A copolymer with polyacrylonitrile as a main component was subjected tospun processing, calcined processing, and surface oxidation treatmentprocessing to obtain a continuous carbon fiber with a total single yarnnumber of 12,000. The characteristics of this continuous carbon fiberwere as follows.

Single filament diameter: 7 μm

Specific gravity: 1.8Tensile strength: 4,600 MPaTensile modulus: 220 GPa

[PP Resin]

A resin sheet with a weight per unit area of 100 g/m² formed of 80% bymass of an unmodified polypropylene resin (“Prime Polypro” (registeredtrademark) J105G manufactured by PRIME POLYMER Co, Ltd.) and 20% by massof an acid-modified polypropylene resin (“ADMER” QB510 manufactured byMitsui Chemicals, Inc.) was prepared. Table 1 lists the characteristicsof the obtained resin sheet.

[PA Resin]

A resin film with a weight per unit area of 124 g/m² formed of a nylon 6resin (“AMILAN” (registered trademark) CM1021T manufactured by TorayIndustries, Inc.) was prepared. Table 1 lists the characteristics of theobtained resin film.

[PC Resin]

A resin film with a weight per unit area of 132 g/m² formed of apolycarbonate resin (“lupilon” (registered trademark) H-4000manufactured by Mitsubishi Engineering-Plastics Corporation) wasprepared. Table 1 lists the characteristics of the obtained resin film.

[PPS Resin]

A resin nonwoven fabric with a weight per unit area of 147 g/m² formedof a polyphenylene sulfide resin (“TORELINA” (registered trademark)M2888 manufactured by Toray Industries, Inc.) was prepared. Table 1lists the characteristics of the obtained resin nonwoven fabric.

[Epoxy Resin]

Blended were 40 parts by mass of “Epototo” YD128 (manufactured by TohtoKasei Co., Ltd.), 20 parts by mass of “Epototo” YD128G (manufactured byTohto Kasei Co., Ltd.), 20 parts by mass of “Epo Tohto” 1001(manufactured by Japan Epoxy Resins Co., Ltd.), and 20 parts by mass of“Epo Tohto” 1009 (manufactured by Japan Epoxy Resins Co., Ltd.) as epoxyresins; 4 parts by mass of DICY 7 (dicyandiamide manufactured by JapanEpoxy Resins Co., Ltd.) and 3 parts by mass of DCMU 99(3-(3,4-dichlorophenyl)-1,1-dimethylurea manufactured by HODOGAYACHEMICAL CO., LTD.) as curing agents; and 5 parts by mass of “Vinylec” K(polyvinyl formal manufactured by CHISSO CORPORATION) as an additive.From this blend, a resin film with a weight per unit area of 132 g/m²was prepared using a knife coater. Table 1 lists the characteristics ofthe obtained resin film.

[Fiber-Reinforced Mat 3]

Carbon Fiber 1 was cut into 6 mm with a strand cutter to obtain choppedcarbon fibers. A dispersion with a concentration of 0.1% by masscontaining water and a surfactant (polyoxyethylene lauryl ether (productname) manufactured by nacalai tesque) was prepared. Using thisdispersion and the chopped carbon fibers, a fiber-reinforced mat wasmanufactured using an apparatus for manufacturing a fiber-reinforced matillustrated in FIG. 6. The manufacturing apparatus illustrated in FIG. 6includes a cylindrical vessel with a diameter of 1,000 mm having anopening cock at the lower part of the vessel as a dispersing tank and alinear transportation unit (an inclination angle of 30°) connecting thedispersing tank and a paper-making tank. A stirrer is attached to anopening at the top face of the dispersing tank. The chopped carbonfibers and the dispersion (a dispersing medium) can be charged from theopening. The paper-making tank is a tank including a mesh conveyorhaving a paper-making face with a width of 500 mm on its bottom, and aconveyor that can convey a carbon fiber substrate (a paper-makingsubstrate) is connected to the mesh conveyor. Paper making was performedwith a carbon fiber concentration in the dispersion of 0.05% by mass.The carbon fiber substrate after paper making was dried for 30 minutesin a drying oven at 200° C. to obtain Fiber-Reinforced Mat 3. Theobtained weight per unit area was 50 g/m². Table 2 lists thecharacteristics of the obtained Fiber-Reinforced Mat 3.

[Fiber-Reinforced Mat 5]

Carbon Fiber 1 was cut into 25 mm with a strand cutter to obtain choppedcarbon fibers. The obtained chopped carbon fibers were caused to fallfreely from a height of 80 cm to obtain Fiber-Reinforced Mat 5 in whichthe chopped carbon fibers were randomly distributed. Table 2 lists thecharacteristics of the obtained Fiber-Reinforced Mat 5.

First Reference Example

A laminate was prepared in which Fiber-Reinforced Mat 3 as afiber-reinforced mat and the PP resin as a resin sheet were arranged inorder of [resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet]. Subsequently, a structure material was obtained through thefollowing processes (I) through (V). In the obtained structure material,voids with the reinforced fibers as columnar supports were found bysectional observation. Table 5 lists the characteristics of the obtainedstructure material.

(I) The laminate is arranged within a mold cavity for press moldingpreheated at 230° C., and the mold is closed.

(II) Subsequently, after being maintained for 120 seconds, the mold ismaintained for additional 60 seconds with a pressure of 3 MPa applied.

(III) After Process (II), the mold cavity is opened, and a metallicspacer is inserted into the end thereof to perform adjustment to give athickness of 3.4 mm when the structure material is obtained.

(IV) Subsequently, the mold cavity is again fastened, and the cavitytemperature is decreased to 50° C. with the pressure maintained.

(V) The mold is opened, and the structure material is taken out of it.

Twenty-First Example

A laminate was obtained in a manner similar to the first referenceexample using a fiber-reinforced mat and a resin sheet similar to thoseof the first reference example. Subsequently, a structure material wasobtained through the following processes (I) through (VI). In theobtained structure material, voids with the reinforced fibers ascolumnar supports were found by sectional observation. Table 5 lists thecharacteristics of the obtained structure material.

(I) The laminate is arranged within a mold cavity for press moldingpreheated at 230° C., and the mold is closed.

(II) Subsequently, after being maintained for 120 seconds, the mold ismaintained for additional 60 seconds with a pressure of 3 MPa applied.

(III) After Process (II), the mold cavity was opened, and a spacer witha thickness of 1.2 mm was inserted into the end thereof, and the moldwas maintained for 5 seconds.

(IV) Subsequently, adjustment is performed to give a thickness of 3.4 mmwhen the structure material is obtained.

(V) Subsequently, the mold cavity is again fastened, and the cavitytemperature is decreased to 50° C. with the pressure maintained.

(VI) The mold is opened, and the structure material is taken out of it.

Twenty-Second Example

A laminate was obtained in a manner similar to the twenty-first exampleusing a fiber-reinforced mat and a resin sheet similar to those of thefirst reference example. Subsequently, a structure material was obtainedthrough the following processes (I) through (VI). In the obtainedstructure material, voids with the reinforced fibers as columnarsupports were found by sectional observation. Table 5 lists thecharacteristics of the obtained structure material.

(I) The laminate is arranged within a mold cavity for press moldingpreheated at 230° C., and the mold is closed.

(II) Subsequently, after being maintained for 120 seconds, the mold ismaintained for additional 60 seconds with a pressure of 3 MPa applied.

(III) After Process (II), the mold cavity was opened, and a metallicspacer with a thickness of 2.0 mm was inserted into the end thereof, andthe mold was maintained for 20 seconds.

(IV) Subsequently, adjustment is performed to give a thickness of 3.4 mmwhen the structure material is obtained.

(V) Subsequently, the mold cavity is again fastened, and the cavitytemperature is decreased to 50° C. with the pressure maintained.

(VI) The mold is opened, and the structure material is taken out of it.

Twenty-Third Example

A laminate was obtained in a manner similar to the twenty-first exampleusing a fiber-reinforced mat and a resin sheet similar to those of thefirst reference example. Subsequently, a structure material was obtainedthrough the following processes (I) through (VI). In the obtainedstructure material, voids with the reinforced fibers as columnarsupports were found by sectional observation. Table 5 lists thecharacteristics of the obtained structure material.

(I) The laminate is arranged within a mold cavity for press moldingpreheated at 230° C., and the mold is closed.

(II) Subsequently, after being maintained for 120 seconds, the mold ismaintained for additional 60 seconds with a pressure of 3 MPa applied.

(III) After Process (II), the mold cavity was opened, and metallicspacers with a thickness of 2.3 mm were inserted at regular intervalsfrom the end to the center thereof, and the mold was maintained for 20seconds.

(IV) Subsequently, the mold cavity is opened, and adjustment isperformed to give a thickness of 3.4 mm of a part not being in contactwith the metallic spacers at Process (III).

(V) Subsequently, the mold cavity is again fastened, and the cavitytemperature is decreased to 50° C. with the pressure maintained.

(VI) The mold is opened, and the structure material is taken out of it.

Twenty-Fourth Example

A structure material was obtained in a manner similar to thetwenty-first example except that the resin sheet was changed from the PPresin to the PA resin, that the preheating temperature at Process (I)was changed from 230° C. to 260° C., that the cavity temperature atProcess (IV) was changed from 50° C. to 60° C., and that the thicknessof the metallic spacer at Process (III) was changed. Table 5 lists thecharacteristics of the obtained structure material.

Twenty-Fifth Example

A structure material was obtained in a manner similar to thetwenty-first example except that the resin sheet was changed from the PPresin to the PPS resin, that the preheating temperature at Process (I)was changed from 230° C. to 300° C., that the cavity temperature atProcess (IV) was changed from 50° C. to 150° C., and that the thicknessof the metallic spacer at Process (III) was changed. Table 5 lists thecharacteristics of the obtained structure material.

Twenty-Sixth Example

A structure material was obtained in a manner similar to thetwenty-first example except that the resin sheet was changed from the PPresin to the PC resin, that the preheating temperature at Process (I)was changed from 230° C. to 300° C., and that the cavity temperature atProcess (IV) was changed from 50° C. to 80° C. Table 5 lists thecharacteristics of the obtained structure material.

Twenty-Seventh Example

A laminate was obtained in a manner similar to the twenty-first examplewith the resin sheet changed from the PP resin to the epoxy resin.Subsequently, a structure material was obtained through the followingprocesses (I) through (VI). In the obtained structure material, voidswith the reinforced fibers as columnar supports were found by sectionalobservation. Table 5 lists the characteristics of the obtained structurematerial.

(I) The laminate is arranged within a mold cavity for press moldingpreheated at 150° C., and the mold is closed.

(II) Subsequently, the mold is maintained for additional 20 seconds witha pressure of 3 MPa applied.

(III) After Process (II), the mold cavity was opened, and a spacer witha thickness of 1.2 mm was inserted into the end thereof, and the moldwas maintained for 5 seconds.

(IV) Subsequently, adjustment is performed to give a thickness of 3.4 mmwhen the structure material is obtained.

(V) Subsequently, the mold cavity is again fastened, and the cavitytemperature is decreased to 50° C. with the pressure maintained.

(VI) The mold is opened, and the structure material is taken out of it.

Eleventh Comparative Example

A laminate was prepared in which Fiber-Reinforced Mat 3 as afiber-reinforced mat and the PP resin as a resin sheet were arranged inorder of [resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet/resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/resin sheet/fiber-reinforced mat/resin sheet/fiber-reinforcedmat/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet/fiber-reinforced mat/resin sheet/fiber-reinforced mat/resinsheet]. Subsequently, a structure material was obtained in a mannersimilar to the twenty-first example except that the metallic spacer wasnot used at Process (III) in the twenty-first example. Table 6 lists thecharacteristics of the obtained structure material.

Twelfth Comparative Example

Seventy pieces of Fiber-Reinforced Mat 3 were stacked on one another,which was put between the PP resin to prepare a laminate. Subsequently,a structure material was obtained in a manner similar to thetwenty-first example except that the thickness of the metallic spacerwas changed from 3.4 mm to 3.2 mm at Process (III) in the twenty-firstexample. Table 6 lists the characteristics of the obtained structurematerial.

Thirteenth Comparative Example

A laminate was prepared in which Fiber-Reinforced Mat 3 as afiber-reinforced mat and the PP resin as a resin sheet were arranged inorder of [resin sheet/fiber-reinforced mat/fiber-reinforced mat/resinsheet]. Subsequently, a structure material was obtained in a mannersimilar to the twenty-first example except that the thickness of themetallic spacer was changed from 3.4 mm to 1.4 mm at Process (III) inthe twenty-first example. Table 6 lists the characteristics of theobtained structure material.

Fourteenth Comparative Example

A laminate was prepared in which Fiber-Reinforced Mat 3 as afiber-reinforced mat and the PP resin as a resin sheet were arranged inorder of [resin sheet/fiber-reinforced mat/fiber-reinforced mat/resinsheet/resin sheet/fiber-reinforced mat/fiber-reinforced mat/resinsheet/resin sheet/fiber-reinforced mat/fiber-reinforced mat/resinsheet]. Subsequently, a structure material was obtained in a mannersimilar to the twenty-first example except that the structure materialwas obtained through the processes (I) through (VI) in the twenty-firstexample. Table 6 lists the characteristics of the obtained structurematerial.

Fifteenth Comparative Example

A structure material was obtained in a manner similar to thetwenty-first example except that Fiber-Reinforced Mat 5 was used as afiber-reinforced mat. Table 6 lists the characteristics of the obtainedstructure material.

Sixteenth Comparative Example

A structure material was obtained in a manner similar to thetwenty-first example except that a molded body only through Process (I)and Process (III) in example 21 was taken out of the mold and wasair-cooled. Table 6 lists the characteristics of the obtained structurematerial.

Seventeenth Comparative Example

A laminate was obtained in a manner similar to the twenty-first exampleusing a fiber-reinforced mat and a resin sheet similar to those of thetwenty-first example. Subsequently, a structure material was obtainedthrough the following processes (I) through (VI). Table 6 lists thecharacteristics of the obtained structure material.

(I) The laminate is arranged within a mold cavity for press moldingpreheated at 230° C., and the mold is closed.

(II) Subsequently, after being maintained for 120 seconds, the mold ismaintained for additional 60 seconds with a pressure of 3 MPa applied.

(III) After Process (II), the mold cavity was opened, and a spacer witha thickness of 1.8 mm was inserted into the end thereof, and the moldwas maintained for 20 seconds.

(IV) Subsequently, adjustment is performed to give a thickness of 3.4 mmwhen the structure material is obtained.

(V) Subsequently, the mold cavity is again fastened, and the cavitytemperature is decreased to 50° C. with the pressure maintained.

(VI) The mold is opened, and the structure material is taken out of it.

TABLE 5 First Twenty- Twenty- Twenty- Twenty- Twenty- Twenty- Twenty-Reference first second third fourth fifth sixth seventh Example ExampleExample Example Example Example Example Example Structure Reinforcedfibers — Fiber- Fiber- Fiber- Fiber- Fiber- Fiber- Fiber- Fiber-material Reinforced Reinforced Reinforced Reinforced Reinforced Rein-Rein- Rein- Mat 3 Mat 3 Mat 3 Mat 3 Mat 3 forced forced forced Mat 3 Mat3 Mat 3 Resin — PP resin PP resin PP resin PP resin PA resin PPS resinPC resin Epoxy resin Volume content of reinforced % by 6.7 — — — — — — —fibers volume Volume content of resin % by 26.6 — — — — — — — volumeVolume content of voids % by 66.7 — — — — — — — volume Volume content ofreinforced % by — 20.0 20.0 20.0 20.0 20.0 20.0 20.0 fibers of firstpart (surface) volume Volume content of resin of first % by — 80.0 80.080.0 80.0 80.0 80.0 80.0 part (surface) volume Porosity of first part(surface) % by — 0 0 0 0 0 0 0 volume Volume content of reinforced % by— 3.3 6.7 6.7 6.7 6.7 6.4 6.4 fibers of second part (center) volumeVolume content of resin of % by — 13.4 26.6 26.6 26.6 26.6 26.9 26.9second part (center) volume Porosity of second part (center) % by — 83.366.7 66.7 66.7 66.7 66.7 66.7 volume Specific gravity of entire g/cm³0.36 0.36 0.50 0.50 0.50 0.71 0.65 0.65 structure material Specificgravity of first part g/cm³ — 1.08 1.08 1.08 1.27 1.44 1.32 1.32(surface) of structure material Specific gravity of second part g/cm³ —0.18 0.36 0.36 0.42 0.48 0.44 0.44 (center) of structure materialThickness of structure material mm 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.3 (St)Length of reinforced fibers (Lf) mm 6 6 6 6 6 6 6 6 Oriented angle insectional ° 4.01 — — — — — — — direction of structure material (θf)Oriented angle of first part of ° — 1.34 2.04 2.04 2.04 2.04 2.04 2.04structure material Oriented angle of second part of ° — 20.01 4.01 4.014.01 4.01 4.01 4.01 structure material Lf² · (1 − cos(θf)) — 0.09 0.360.09 0.09 0.10 0.10 0.10 0.10 Resin coating around reinforced PresentPresent Present Present Present Present Present Present Present fibersor absent Resin thickness around μm 4.8 4.8 4.8 4.8 4.8 4.6 5.2 5.2reinforced fibers Bending modulus (Ec) GPa 8.1 8.1 8.7 — 9.7 10.0 9.010.2 Specific bending modulus — 5.58 5.58 4.11 — 4.27 3.03 3.20 3.34Specific bending modulus of — — 2.90 2.90 2.90 2.60 2.50 2.40 2.50 firstpart Specific bending modulus of — — 8.82 5.58 5.58 5.58 5.58 5.58 4.81second part

TABLE 6 Eleventh Twelfth Thirteenth Fourteenth Fifteenth SixteenthSeventeenth Comparative Comparative Comparative Comparative ComparativeComparative Comparative Example Example Example Example Example ExampleExample Structure Reinforced fibers — Fiber- Fiber- Fiber- Fiber- Fiber-Fiber- Fiber- material Reinforced Reinforced Reinforced ReinforcedReinforced Reinforced Reinforced Mat 3 Mat 3 Mat 3 Mat 3 Mat 5 Mat 3 Mat3 Resin — PP resin PP resin PP resin PP resin PP resin PP resin PP resinVolume content of reinforced fibers % by 20 60 3.3 3.3 6.7 6.7 6.7volume Volume content of resin % by 80 6.7 13.4 13.4 26.6 26.6 26.6volume Volume content of voids % by 0 33.3 83.3 83.3 66.7 66.7 66.7volume Porosity of first part (surface) of % by 0 33.3 83.3 83.3 66.766.7 33.3 structure material volume Porosity of second part (center) of% by 0 33.3 83.3 83.3 66.7 66.7 83.3 structure material volume Specificgravity of entire structure g/cm³ 1.08 1.14 0.18 0.18 0.42 0.36 0.36material Specific gravity of first part g/cm³ 1.08 1.14 0.18 0.18 0.420.36 0.72 (surface) of structure material Specific gravity of secondpart g/cm³ 1.08 1.14 0.18 0.18 0.42 0.36 0.18 (center) of structurematerial Thickness of structure material (St) mm 2.8 3.2 1.4 3.4 3.4 3.43.4 Length of reinforced fibers (Lf) mm 6 6 5 5 0.5 6 6 Oriented anglein sectional direction ° 1.34 0.65 8.04 8.04 55.6 4.01 2.04 of structurematerial (θf) Oriented angle of first part of ° 1.34 0.65 8.04 8.04 55.64.01 2.04 structure material Oriented angle of second part of ° 1.340.65 8.04 8.04 55.6 4.01 8.04 structure material Lf² · (1 − cos(θf)) —0.01 0.00 0.25 0.25 0.12 0.09 0.02 Resin coating around Present CompleteAbsent Partially Partially Partially Absent Partially reinforced fibersor impregnation present present present present absent Resin thicknessaround reinforced μm — Unmeasurable 0.5 to 30 0.5 to 30 20 Adherence 0.5to 30 fibers (only partially) with uneven with uneven only to withuneven density density inter- density sections of reinforced fibersBending modulus (Ec) GPa 14.0 0.2 1.2 1.2 2.5 1.0 2.5 Specific bendingmodulus — 2.23 0.51 5.90 5.90 3.23 2.78 3.23 Specific bending modulus offirst part — — — — — — — 2.80 Specific bending modulus — — — — — — —4.04 of second part

[Consideration]

It is clear that the present example is excellent in a balance betweenthe specific bending modulus and the absolute value of the bendingmodulus owing to the fact that the thickness St of the structurematerial satisfies the conditional expression St≥Lf²·(1−cos(θf)).Furthermore, the same holds true for the twenty-fourth, thetwenty-fifth, and the twenty-sixth examples, in which the resin type waschanged. In contrast, in the eleventh comparative example, in which thefiber-reinforced mat and the resin were similar to those of thetwenty-first example, owing to the absence of voids, the specificbending modulus was unable to be satisfied. In the twelfth comparativeexample, in which the volume ratios of the resin and the voids wereadjusted, a balance between them and the volume ratio of thefiber-reinforced mat was poor, and the bending modulus was low. It isestimated that this is because coating by the resin around thereinforced fibers was not formed. In the thirteenth comparative example,the bending modulus was low. This is because the reinforced fibers notin a nearly monofilament form were used, which was not improved by thefourteenth comparative example, in which the thickness of the structurematerial was changed. In the fifteenth comparative example, the fiberlength of the reinforced fibers was reduced, and the conditionalexpression St≥Lf²·(1−cos(θf)) was unable to be satisfied. Consequently,the absolute value of the bending modulus was unable to be satisfied. Inthe sixteenth comparative example, the reinforced fibers were not coatedwith the resin, and the resin was localized at intersection points ofthe reinforced fibers, whereby the absolute value of the bending moduluswas low, although the contents of the reinforced fibers, the resin, andthe voids were satisfied; as a result, the value of the specific bendingmodulus was unable to be satisfied. In the seventeenth comparativeexample, high-specific gravity regions were provided on the surfaces,whereas a low specific gravity region was provided at the central part;their thickness ratio was 1:1 between both surfaces and the center. Thebending properties of the seventeenth comparative example wereevaluated; owing to a bad balance in thickness ratio between the regionshaving voids on the surfaces and the region having voids at the centerof the structure material, the properties of the layer having a highporosity at the central part were predominant, which made unable toobtain a desired property.

INDUSTRIAL APPLICABILITY

The present invention can provide a structure material excellent instiffness and lightness. In addition, the present invention can providea structure material excellent in lightness and mechanicalcharacteristics.

REFERENCE SIGNS LIST

-   -   1 Structure material    -   2 Resin    -   3 Reinforced fiber    -   4 Void

1. A structure material comprising a resin, reinforced fibers, and voids, a volume content of the resin being within a range of 2.5% by volume or more and 85% by volume or less, a volume content of the reinforced fibers being within a range of 0.5% by volume or more and 55% by volume or less, the voids being contained in the structure material in a rate within a range of 10% by volume or more and 97% by volume or less, a thickness St of the structure material satisfying a conditional expression: St≥Lf²·(1−cos(θf)) where a length of the reinforced fibers is Lf and an oriented angle of the reinforced fibers in a sectional direction of the structure material is θf, and a specific bending modulus of the structure material represented as Ec^(1/3), ρ⁻¹ being within a range of 3 or more and 20 or less where a bending modulus of the structure material is Ec and a specific gravity of the structure material is ρ, and the bending modulus Ec of the structure material being 3 GPa or more.
 2. A structure material comprising a resin, reinforced fibers, and voids, a volume content of the resin being within a range of 2.5% by volume or more and 85% by volume or less, a volume content of the reinforced fibers being within a range of 0.5% by volume or more and 55% by volume or less, the voids being contained in the structure material in a rate within a range of 10% by volume or more and 97% by volume or less, a thickness St of the structure material satisfying a conditional expression: St≥Lf²·(1−cos(θf)) where a length of the reinforced fibers is Lf and an oriented angle of the reinforced fibers in a sectional direction of the structure material is θf, a specific bending modulus of a first part of the structure material represented as Ec^(1/3)·ρ⁻¹ being within a range of 1 or more and less than 3 where a bending modulus of the structure material is Ec and a specific gravity of the structure material is ρ, and a specific bending modulus of a second part of the structure material different from the first part being within a range of 3 or more and 20 or less.
 3. The structure material according to claim 1, wherein the bending modulus Ec of the structure material is 6 GPa or more.
 4. The structure material according to claim 2, wherein the bending modulus Ec of the second part of the structure material is 6 GPa or more.
 5. The structure material according to claim 2, wherein the first part and the second part of the structure material are present at different positions in a thickness direction of the structure material.
 6. The structure material according to claim 2, wherein the first part and the second part of the structure material are present at different positions in a planar direction of the structure material.
 7. The structure material according to claim 1, wherein a specific gravity ρ of the structure material is 0.9 g/cm³ or less.
 8. The structure material according to claim 1, wherein a porosity of parts within 30% to a midpoint position in a thickness direction from surfaces of the structure material is within a range of 0% by volume or more and less than 10% by volume, and a porosity of a residual part is within a range of 10% by volume or more and 97% by volume or less.
 9. The structure material according to claim 1, wherein the reinforced fibers are coated with the resin, and a thickness of the resin is within a range of 1 μm or more and 15 μM or less.
 10. The structure material according to claim 1, wherein the reinforced fibers are discontinuous and are dispersed in a nearly monofilament form and in a random manner.
 11. The structure material according to claim 1, wherein an oriented angle θf of the reinforced fibers in the structure material is 3° or more.
 12. The structure material according to claim 1, wherein a longer of the mass mean fiber length of the reinforced fibers is within a range of 1 mm or more and 15 mm or less.
 13. The structure material according to claim 1, wherein the reinforced fibers are carbon fibers.
 14. The structure material according to claim 1, wherein the resin contains at least one thermoplastic resin.
 15. The structure material according to claim 1, wherein the resin contains at least one thermosetting resin. 